Beirut (AFP) - Russian warplanes carried out intense air strikes on rebel strongholds in Syria on Friday hours before a ceasefire was due to come into force, the Syrian Observatory for Human Rights monitor said.
Russia dismissed the reports and said it was continuing strikes on "terrorist organisations" ahead of the truce.
The partial ceasefire between regime forces and non-jihadist rebel fighters is due to take effect at midnight Friday (2200 GMT) Damascus time. It does not include the Islamic State jihadist group and the Al-Qaeda affiliated Al-Nusra Front.
"From last night to this morning there have been Russian air strikes that are more intense than usual on rebel bastions including on Eastern Ghouta east of Damascus, in the north of Homs province and in the west of Aleppo province," Observatory head Rami Abdel Rahman said.
Air strikes in the non-jihadist rebel-held Qabtan al-Jabal area of Aleppo province killed eight members of the same family including three children on Thursday night, the monitor said.
"There were at least 25 air strikes on Eastern Ghouta," a main rebel bastion where the predominant opposition faction is the Jaish al-Islam movement, Abdel Rahman said.
"At least 10 of those hit Douma", an area there, said the Britain-based monitor, which relies of a wide network of sources in Syria.
"At the same time regime forces have violently shelled the city," Abdel Rahman said.
"It's more intense than usual. It's as if they (the Russians and the regime) want to subdue rebels in these regions or score points before the ceasefire," he said.
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Russian air strikes also hit the Daret Ezza area in western Aleppo province and Talbisseh city in Homs province.
In these areas, as in Ghouta, rebels outnumber Nusra fighters, the monitor said.
Kremlin spokesman Dmitry Peskov dismissed the Observatory's reports.
"The Russian air force is certainly continuing its operation in Syria" but against "terrorist organisations," he said.
Since Moscow launched air strikes in Syria in September, it has been accused of hitting non-jihadist rebel groups in support of the Damascus regime, a longtime ally.
Abdel Rahman said the implementation of the partial truce will be complicated as Nusra are allied with rebels -- Islamist and non-Islamist -- in several parts of Syria.
Their "territories overlap especially in Idlib and Aleppo provinces. It will be very complex," Abdel Rahman said.
More than 270,000 people have been killed since the war erupted in March 2011, and millions have fled their homes.
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Intense Russian air strikes battered rebel bastions across Syria on Friday, a monitor said, just hours before a midnight deadline for a landmark ceasefire in the country's five-year civil war.
With the ceasefire due to take effect at 2200 GMT on Friday, US President Barack Obama has warned Damascus and key ally Moscow that the "world will be watching".
Both President Bashar al-Assad's regime and the main opposition body have agreed to the deal -- which allows fighting to continue against the Islamic State (IS) group and other jihadists.
The agreement brokered by Russia and the United States marks the biggest diplomatic push yet to help end Syria's violence, but has been plagued by doubts after the failure of previous peace efforts.
Members of the 17-nation group backing the process are to meet in Geneva on Friday to work out further details of the so-called "cessation of hostilities", which is then expected to be endorsed by the UN Security Council, diplomats said.
The Syrian Observatory for Human Rights, a Britain-based monitor, said Russia and the regime had launched a wave of attacks on non-jihadist rebel areas ahead of the deadline.
"It's more intense than usual. It's as if they want to subdue rebels in these regions or score points before the ceasefire," Observatory head Rami Abdel Rahman said.
Russia launched air strikes in Syria last September saying it was targeting "terrorists" but critics have accused Moscow of hitting rebel forces in support of Assad, a longtime ally.
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Syrian men carry a body outside a makeshift hospital following reported air strikes in the city of A …
- Complex battlefields -
The Observatory said there had been Russian strikes overnight on rebel bastions including the Eastern Ghouta region outside Damascus, the north of Homs province and the west of Aleppo province.
There was also intense regime shelling of the rebel-held city of Douma in Eastern Ghouta, he said.
The Kremlin dismissed reports of attacks on non-jihadist rebels.
"The Russian air force is certainly continuing its operation in Syria" but against "terrorist organisations," Kremlin spokesman Dmitry Peskov said.
The intensified attacks prompted Turkey, a key supporter of opposition forces, to express worries over the viability of the ceasefire.
"We are seriously concerned over the future of the ceasefire because of the continuing Russian air raids and ground attacks by forces of Assad," presidential spokesman Ibrahim Kalin told reporters in Ankara.
The complexity of Syria's battlefields -- where moderate and Islamist rebel forces often fight alongside jihadist groups like the Al-Qaeda affiliated Al-Nusra Front -- has raised serious doubts about the feasibility of a ceasefire.
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Russian President Vladimir Putin says Syria peaceplan is "complicated" (AFP Photo/Michail …
Diplomats are reported to be working to define areas that will fall under the partial truce and to set up monitoring mechanisms.
The UN's Syria envoy has said he hopes the agreement will lead to a resumption of peace talks which collapsed earlier this month in Geneva.
Russia and the United States are on opposing sides of the conflict, with Moscow backing Assad and Washington supporting the opposition, but the two powers have been making a concerted push for the ceasefire to be respected.
Russian President Vladimir Putin has promised to do "whatever is necessary" to ensure the ceasefire is implemented. Iran, another key Assad ally, has said it is confident the regime will respect the agreement.
Huddling with his national security advisors in Washington on Thursday, Obama put the onus for upholding the ceasefire firmly on the regime and Russia.
- Doubts, pessimism -
He said he was not "under any illusions" about possible pitfalls, but that the ceasefire could help bring about an end to the war.
"A lot of that is going to depend on whether the Syrian regime, Russia, and their allies live up to their commitments," Obama said.
"The coming days will be critical, and the world will be watching."
Obama also said the US-coalition that launched air strikes against IS in Syria and Iraq in 2014 was making progress, citing territorial gains.
"More people are realising that ISIL is not a caliphate, it's a crime ring," he said, using an alternative acronym for the group.
US Secretary of State John Kerry has been a major booster of the ceasefire but others in Washington have been less optimistic about the chances of ending a conflict that has left more than 270,000 dead and forced millions from their homes.
"There's pessimism, not expectation, pessimism," a senior US official told AFP, citing what he said was Russia's history of making then breaking ceasefire commitments in conflicts in Georgia and Ukraine.
"What real incentives do the Russians have to act in good faith?" asked Shadi Hamid, a Middle East expert and a senior fellow at the Brookings Institution.
"There is no credible threat of military force and without a credible threat of military force, the Russians are going to act like they have been acting for the past several years."
Kerry has warned that Washington is considering a "Plan B" to deal with Syria if the ongoing efforts fail, but has not provided any details.