Scores of rebel groups sign up to ceasefire, but Russian bombing 'more intense'

Almost 100 rebel factions in Syria have agreed to respect a temporary ceasefire negotiated by the US and Russia that is due to take effect at midnight local time (10.00 pm GMT), the country's main opposition group said on Friday.

"Factions of the Free Syrian Army and the armed opposition agree to respect a temporary truce... for two weeks," the High Negotiations Committee said in a statement, referring to "97 factions from the opposition".

Russian warplanes continued to carry out intense air strikes on rebel strongholds in Syria hours before a ceasefire is due to come into force, the UK-based Syrian Observatory for Human Rights monitor said.

"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-militant 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.

Abdel Rahman also reported that there were at least 25 air strikes on Eastern Ghouta where Jaish al-Islam is the predominant opposition faction. Simultaneously, he said, the government shelled the city of Douma.

"It's more intense than usual. It's as if they (the Russians and the government) want to subdue rebels in these regions or score points before the ceasefire," Abdel Rahman said.

A spokesperson for the Kremlin said Russia was continuing operations against "terrorist organisations" but dismissed the Observatory's reporting as unreliable.

Reports of the latest airstrikes came hours after US President Barack Obama warned Moscow and Damascus the "world will be watching" their commitment to a looming ceasefire, as the 17-nation group backing the Syria peace process prepared to fine-tune the deal.

The deal, which excludes the Islamic State (IS) group and the al-Qaeda-affiliated Nusra Front which are recognised as terrorists by the United Nations, 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 were meeting in Geneva on Friday to work out further details of the agreement, which is expected to be endorsed by the UN Security Council on the same day, diplomats said.

There are hopes a successful "cessation of hostilities" will lead to the resumption of peace talks that collapsed in Geneva earlier this month.

"Tomorrow is going to be a very important, I will say a crucial day," the UN's Syria envoy Staffan de Mistura told reporters at the UN's European headquarters in Geneva on Thursday.

Obama said he was certain that groups excluded from the deal would continue to fight, but stressed the US-led coalition was winning the war against IS, citing territorial gains.

He also 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."

Russian President Vladimir Putin has promised to do "whatever is necessary" to ensure the ceasefire is implemented.