Syria has said it is ready to swap prisoners with the rebels and would take swift steps that could lead to the first such mass exchange in nearly three years of fighting.

The announcement was made by Syrian Foreign Minister Walid Muallem in Moscow.

It could mark another diplomatic success for Russia after it managed to convince Syria to renounce its chemical weapons in order to avert imminent US air strikes.

It also came just as the war-torn country's divided opposition prepared to hold decisive talks in Istanbul on whether to join a peace conference that is due to begin on Wednesday in Switzerland.

Mr Muallem failed to specify how many prisoners such a swap would involve or when it might begin.

But it would represent a concession to one of the opposition's key demands before it agreed to peace talks.

"I informed (Russian Foreign Minister Sergei) Lavrov of our principled position in favour of an agreement to exchange those held in Syrian prisons for those taken by the other side," Mr Muallem said following talks with his Russian counterpart.

"We are ready to exchange lists and develop the necessary mechanism for accomplishing these goals," Mr Muallem said.

He also confirmed his government's plans to send a senior delegation to the Swiss lakeside city of Montreux where the long-delayed peace conference, the first since June 2012, is due to begin.

Syria "will take part in Geneva II and make every effort to ensure this event is a success and meets the aspirations of the Syrian people and the direct orders of President Bashar al-Assad," said Mr Muallem.

He said Mr Assad will send his representatives to Switzerland "irrespective of the situation around the participation or the non-participation of the National Coalition at this conference".

US Secretary of State John Kerry yesterday also called the umbrella rebel group not to boycott the talks because they represented "the best opportunity for the opposition to achieve the goals of the Syrian people and the revolution".

Plans for the peace conference were first announced in May by Mr Kerry and Mr Lavrov in Moscow amid indications that a war that has now claimed 130,000 lives had reached a stalemate.

But more recent government advances have put the rebels at a disadvantage at any negotiations.

They have also been increasingly divided by rivalries between jihadists and more mainstream Islamists, as well as among groups with allegiance to Saudi Arabia and those getting military and financial backing from Qatar.

Mr Lavrov and Mr Kerry this week also issued a joint call for Syria's regime and the rebels to agree to ceasefires in parts of their battle-scarred country that could begin in the devastated northern city of Aleppo.

Mr Muallem did not address the ceasefire call directly, but said he had handed Mr Lavrov "a plan concerning measures for ensuring security in Aleppo".

Mr Lavrov said Mr Muallem had informed him of Mr Assad's readiness "to take a series of humanitarian steps" that would lead to the speedy delivery of assistance to those suffering from the three-year civil war.

"This concerns specific proposals that are already being implemented concerning the delivery of humanitarian supplies to settlements in the Eastern Ghuta region and other areas, including the suburbs of Damascus and Aleppo," Mr Lavrov said.

UN Secretary General Ban Ki-moon has confirmed that he will attend the conference.