Rebel groups in Syria have told the BBC they will not stop fighting because they do not believe that Russia will end its bombing campaign in support of the government.

They have expressed scepticism over a deal by world powers to push for a cessation of hostilities within a week.

They have also reiterated their demand that President Bashar al-Assad be removed from power.

Earlier the president said he wanted to retake "the whole country" from rebels.

Three Syrian rebel groups have expressed doubts to the BBC over the cessation of hostilities agreement:

* A spokesman for the Free Syrian Army said: "We remain sceptical all the time about the Russians."

* The conservative Ahrar al-Sham group said that it would not stop fighting until government shelling stopped, safe border crossings were opened for civilians, prisoners released and besieged areas relieved

* Faylaq al-Sham - part of a coalition of seven different groups operating in the north - said that it would not relinquish its weapons until President Assad was removed

Riad Hijab, co-ordinator of Syria's main opposition bloc, earlier told the BBC's Newsnight programme that to announce a cessation of hostilities before making progress in the political process "is not realistic, objective or logical".

Agreement to try to bring about a cessation of hostilities and allow more access for humanitarian aid was reached by world powers late on Thursday in Germany, but neither the Syrian government nor the rebels were involved.

So far there has been no sign of the UN realising its hopes of delivering aid imminently to more besieged areas.

A new UN task force set up to co-ordinate aid distributions convened in Geneva on Friday.

Some Syrian cities have been cut off from aid for more than a year because of fighting. About 13.5 million people are in need, the UN says.

(BBC)