Russia continues Syria strikes ahead of ceasefire: Kremlin

Russian warplanes continued to bomb "terrorist organisations" in Syria hours before a ceasefire goes into effect, the Kremlin said Friday, denying reports it was mounting intense strikes on rebel strongholds.

"The Russian air force is certainly continuing its operation in Syria" against "terrorist organisations", Kremlin spokesman Dmitry Peskov said after the Syrian Observatory for Human Rights said Russian warplanes were still targeting rebels ahead of 2200 GMT truce.

Observatory head Rami Abdel Rahman said the air strikes were "more intense than usual" and targeted rebel bastions, including in Eastern Ghouta east of Damascus, northern Homs province and the west of Aleppo province.

But Peskov said reports by the Syrian Observatory had never been reliable, saying it had "repeatedly given out information which, unfortunately, had not been confirmed and had not been corroborated by any data".

Peskov said Russia was focusing its firepower on the Islamic State, Al-Nusra Front and other extremist groups designated as legitimate targets by the UN Security Council, and would continue doing so after the ceasefire takes hold.

"This is one of the conditions of an initiative agreed by the presidents of Russia and the United States," he added.

The ceasefire agreement brokered by Moscow and Washington calls for a "cessation of hostilities" between Russian-backed President Bashar al-Assad's forces and opposition groups from midnight Friday Damascus time (2200 GMT).

But many fear Russia will keep pounding moderate rebels fighting Assad's regime, under the cover of fighting "terrorism".

US Secretary of State John Kerry has warned that Washington is considering a "Plan B" if Damascus and Moscow do not keep their end of the bargain.

Russian Foreign Minister Sergei Lavrov said on Friday that for the ceasefire to work, the US-led coalition should abstain from talk about "some sort of Plan B, about preparing a ground operation, about the creation of some sort of useless buffer zones".

Speaking after talks with Arab League chief Nabil al-Arabi, Russia's top diplomat also took issue with the fact that Syria's main opposition grouping said it would respect the ceasefire "for two weeks" only.

"The Russian-American initiative does not foresee any preliminary conditions and qualifications," Lavrov said.

He also faulted US President Barack Obama for reiterating on Thursday that Assad should step down if a lasting peace is to be found.

"This completely contradicts all those decisions which the United States signed off on at the UN Security Council," Lavrov said.