London (AFP) - Police Tuesday urged people to identify "aspiring terrorists" among their family members, friends and neighbours after the killing of US journalist James Foley, apparently by a man with an English accent.

The appeal also comes amid growing government concern that British passport holders who travel to fight in Iraq and Syria could return to carry out attacks on home soil.

Jihadist group the Islamic State (IS) posted a graphic video online last week showing the beheading of Foley, who had been missing since his 2012 capture in Syria.

"We are appealing to the public, family members and friends to help identify aspiring terrorists; they may be about to travel abroad, have just returned or be showing signs of becoming radicalised," said Scotland Yard Assistant Commissioner Mark Rowley, the country's most senior police officer on counter-terrorism, in a statement.

"Every reasonable person in the country has been touched by the pitiless murder of James Foley at the hands of Islamic State terrorists, and the murderer's apparent British nationality has focused attention on extremism in the UK as well as the Middle East."

He said British police had arrested five times more people in the first half of this year compared with 2013 for "Syria-related" offences.

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This undated file still image from video released April 7, 2011, by GlobalPost, shows James Foley of …

There were 69 arrests in the first half of 2014 on suspicion of offences including travelling abroad for terrorist training, preparing acts of terrorism and fundraising for terrorist activity.

Some 1,100 pieces of extremist material are also being removed from social media websites such as YouTube, Facebook and Twitter, he added, 800 of them relating to Syria or Iraq.

Intelligence services say 500 Britons have travelled to Syria or Iraq to fight alongside jihadists in the last few years.

The government is under increasing pressure to take steps to combat radicalisation and Home Secretary Theresa May said Saturday that she was considering introducing new powers.

Foreign Secretary Philip Hammond on Sunday called it an "utter betrayal" that the killing had apparently been carried out by a Briton.

Rowley also said that "significant progress" was being made in the hunt for Foley's killer and Britain's ambassador to the US, Peter Westmacott, told CNN Sunday that the country's authorities were "close" to identifying the man.

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LONDON -- It is not just American citizens fighting along the Islamic State of Iraq and Syria, the extremist group known as ISIS.

British citizens are doing the same. One is suspected in the murder of an American journalist.

CBS News looked at how Britain became a center for terrorist recruitment.

At home in Britain, he was Nasser Muthanna, a gifted 20-year-old who once dreamed of becoming a doctor. But in Syria, he is now Abu Muthanna al-Yemeni - one of hundreds of young men who have left the U.K. to join the brutal terrorist group ISIS.

The execution of American journalist James Foley, apparently at the hands of a British citizen, has left Britain struggling to understand how one of its own could be responsible for such an atrocity.

Shiraz Maher is an analyst at the International Center for the Study of Radicalization.

"It was a shocking thing to see but it wasn't surprising. If you look at British fighters in Syria over the last year, we've seen them operate as suicide bombers. We've seen them execute prisoners of war. They are participating in most of the brutal acts out there," Maher said.

He said these men no longer see themselves as being British.

"They've disengaged from British society, they've disengaged from British values, they've bought into something else -- a different identity," Maher said.

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They see themselves as defenders of Islam in a war against nonbelievers. Their barbaric tactics have been glamorized on social media, a powerful recruitment tool that British authorities are now trying to crack down on.

But the challenge is a formidable one. With every victory on the battlefield, ISIS' appeal grows. Many are concerned that it is only a matter of time before their jihad spreads beyond the Middle East.

On a video posted on YouTube, ISIS foreign fighters are seen burning their passport.

"This is a message for to Canada and all the American power-elite, we are coming and we will destroy you," one jihadi says on the video.

"We are coming for you, Barack Obama!" he adds.

One thing that is striking about these jihadis is that some of them are religious novices. Two fighters who came from Britain reportedly purchased copies of "Islam for Dummies" on Amazon. So they don't necessarily have a sophisticated understanding of Islamic theology. They are drawn to the idea of being warriors.

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Intelligence officials closing in on James Foley's killer

A third American hostage held by ISIShas been identified as a 26-year-old American woman who was kidnapped a year ago while doing humanitarian relief work in Syria. The terror group is demanding $6.6 million and the release of U.S. prisoners for the life of the young woman, who the family requested not be identified.

She is the third of at least four Americans who were known to be held by ISIS, the Islamic State of Iraq and Syria. American journalist James Foley was executed by the group in a video that appeared online last week. Another writer, Steven Sotloff, was seen alive but under duress in the same footage.

In addition to the multi-million dollar ransom, the terror group has also demanded that the U.S. release Aafia Siddiqui, an MIT-trained neuroscientist who was convicted by the U.S. in 2010 of trying to kill U.S. officials two years before, according to a supporter of Siddiqui who has been in contact with the hostage’s family.

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ISIS Demands $6.6M Ransom for 26-Year-Old American Woman (ABC News)

Siddiqui’s release has been a regular demand of groups critical of U.S. policy in the Middle East and Southwest Asia, but Monday Siddiqui’s family spoke out through supporters to say they were “very distraught” Siddiqui’s name was invoked with the ransom request and sought to distance themselves from ISIS.

“If the issue is true, we would like to state that our family does not have any connections to such groups or actions,” reads a letter written by Siddiqui’s family. “We believe in a struggle that is peaceful and dignified. Associating Aafia’s name with acts of violence is against everything we are struggling for.”

“While we deeply appreciate the sincere feelings of those who, like us, wish to see the freedom of our beloved Aafia, we cannot agree with a ‘by any means necessary’ approach to Aafia’s freedom. Nor can we accept that someone else’s daughter or sister suffer like Aafia is suffering,” the letter says.

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The Siddiqui family has been “traumatized by the thoughts that someone else could be harmed in the name of Aafia,” said Mauri Saalakhan of the Peace and Justice Foundation, who held a sparsely attended press conference Monday and spoke on behalf of the Siddiqui family.

“They’re opposed to it. In their letter to ISIS they made it very clear, this is not the way, these are not the conditions under which we want our loved ones released,” Saalakhan said. “Nor did they want harm to come to anyone else’s loved one in the name of Aafia… They conveyed that message loud and clear.

“The most important message that I could convey to ISIS or whoever it is that’s holding these innocent people captive abroad is that at the end of the day, this type of approach in response to an injustice that you feel, is not only not the inappropriate way to go, but, properly understood, it is a violation of the tenets of the faith that we claim to believe in,” he said. “We just have to do the right thing because it is the right thing, without any strings attached.. And the right thing would be to let this young woman go back to her family, go back to her life. And the right thing for America to do, for our government… would be to do the same with Dr. Aafia Siddiqui.”

The details of the ISIS ransom demand and the abduction of the young aid worker were disclosed by Saalakhan and a close friend of the unnamed hostage family in statements to ABC News Monday.

Each of the three known surviving American hostages in ISIS’s hands have been threatened with death since Foley’s execution, sources have told ABC News. In the video that showed Foley’s death, a masked militant said that Sotloff’s fate rested in President Obama’s hands – an apparent demand that the U.S. stop airstrikes against ISIS targets in Iraq.

The day after Foley’s execution video emerged online, the U.S. military announced it had continued bombing runs against ISIS in Iraq and overnight The New York Times reportedPresident Obama has approved surveillance flights over Syria, what the paper called a potential precursor to airstrikes there.

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Distraught family members of American Douglas McAuthur McCain, killed in Syria after allegedly joining forces with a militant group, spoke to news outlets and turned to social media Tuesday to express shock and sadness and in some cases, to defend their relative.

U.S. officials confirmed McCain's death in Syria Tuesday and said he had traveled there to fight with an extremist organization, likely the Islamic State of Iraq and the Levant.

"We were aware of U.S. Citizen Douglas McAuthur McCain's presence in Syria and can confirm his death," U.S. National Security Council spokeswoman Caitlin Hayden said in a statement posted by Reuters.

NBC News first reported that McCain had been killed in Syria in a battle between two opposition groups and said it had seen images of his body, bearing a unique neck tattoo, and his passport to verify his identity.

McCain's family expressed disbelief over news of his alleged ties to the violent extremist group ISIL, which last week posted a video of the beheading last week of American journalist James Foley.

Kenneth McCain, an uncle, told CNN's Jim Sciutto that his family is "devastated" and that they were "just as surprised as the country" over reports of Douglas McCain's connection to ISIL.

McCain was born in Illinois, grew up and attended high school in Minnesota and later moved to San Diego, according to published reports. Two cousins still living in Minnesota spoke to the Minneapolis Star Tribune Tuesday and said they had been in touch with McCain as recently as Friday. He told them he was in Turkey.

Kenyata McCain said she noticed some posts on her cousin's Facebook page supporting ISIL, also called ISIS and the Islamic State. His Facebook page was taken down Tuesday.

“I know that he had strong Muslim beliefs, but I didn’t know that he was in support of ISIS. I didn’t think he would be," she said.

Another cousin who requested anonymity said his cousin was not a "radical," adding McCain worked as a caregiver for people with special needs in California and that he had a infant daughter about to turn one.

“I don’t know what he went over there for, I don’t want people to get the idea that he was some kind of monster," he said.

Delecia McCain, who identified herself as Douglas McCain’s sister, posted to Facebook late Tuesday afternoon expressing shock at the loss of her oldest brother.

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Pictured above, a post from the Facebook page of Delecia McCain, who identified herself in comments on the social …

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WASHINGTON (AP) — Global warming is here, human-caused and probably already dangerous — and it's increasingly likely that the heating trend could be irreversible, a draft of a new international science report says.

The United Nations' Intergovernmental Panel on Climate Change on Monday sent governments a final draft of its synthesis report, which combines three earlier, gigantic documents by the Nobel Prize-winning group. There is little in the report that wasn't in the other more-detailed versions, but the language is more stark and the report attempts to connect the different scientific disciplines studying problems caused by the burning of fossil fuels, such as coal, oil and gas.

The 127-page draft, obtained by The Associated Press, paints a harsh warning of what's causing global warming and what it will do to humans and the environment. It also describes what can be done about it.

"Continued emission of greenhouse gases will cause further warming and long-lasting changes in all components of the climate system, increasing the likelihood of severe, pervasive and irreversible impacts for people and ecosystems," the report says. The final report will be issued after governments and scientists go over the draft line by line in an October conference in Copenhagen.

Depending on circumstances and values, "currently observed impacts might already be considered dangerous," the report says. It mentions extreme weather and rising sea levels, such as heat waves, flooding and droughts. It even raises, as an earlier report did, the idea that climate change will worsen violent conflicts and refugee problems and could hinder efforts to grow more food. And ocean acidification, which comes from the added carbon absorbed by oceans, will harm marine life, it says.

Without changes in greenhouse gas emissions, "climate change risks are likely to be high or very high by the end of the 21st century," the report says.

In 2009, countries across the globe set a goal of limiting global warming to about another 2 degrees Fahrenheit above current levels. But the report says that it is looking more likely that the world will shoot past that point. Limiting warming to that much is possible but would require dramatic and immediate cuts in carbon dioxide pollution.

The report says if the world continues to spew greenhouse gases at its accelerating rate, it's likely that by mid-century temperatures will increase by about another 3.6 degrees Fahrenheit (2 degrees Celsius) compared to temperatures from 1986 to 2005. And by the end of the century, that scenario will bring temperatures that are about 6.7 degrees warmer (3.7 degrees Celsius).

"The report tells us once again what we know with a greater degree of certainty: that climate change is real, it is caused by us, and it is already causing substantial damage to us and our environment," Pennsylvania State University climate scientist Michael Mann wrote in an email. "If there is one take home point of this report it is this: We have to act now."

John Christy of the University of Alabama, Huntsville, is in the tiny minority of scientists who are skeptical of mainstream science's claim that global warming is a major problem. He says people will do OK: "Humans are clever. We shall adapt to whatever happens."

While projections show that the world will warm and climate will change, there's still a level of uncertainty about how much, and that makes the problem all about how much risk we accept, said MIT climate scientist Kerry Emanuel.

If it's soon and only a little risk, he said, that's not too bad, but when you look at the risk curve the other end of it is "very frightening."

The report used the word risk 351 times in just 127 pages.

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Online:

Intergovernmental Panel on Climate Change: http://www.ipcc.ch/

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Seth Borenstein can be followed at http://twitter.com/borenbears