Syria's opposition said on Wednesday it supported the idea of a temporary two-week truce to test the seriousness of the other side's commitment to a US-Russian plan for a cessation of hostilities.
The Saudi-backed High Negotiations Committee said it "views a temporary two-week truce as a chance to establish how serious the other side is in committing to the points of the agreement."
"The Committee put down a series of observations to ensure the success of the truce," it added.
HNC, which is the main umbrella organisation for political and armed opponents of the Bashar al Assad regime, said on Monday in a statement that it had "given its acceptance of international efforts for a cessation of hostilities."
But it said acceptance of the deal was conditional on fulfillment of previous demands including an end to blockades, free access for humanitarian aid, release of detainees, and a halt to aerial and artillery bombardments against civilians.
An HNC spokesman said on Tuesday the US-Russian plan for a "cessation of hostilities" included "obscure terms" and was heavily influenced by Russia, which is mounting air strikes in support of Assad.
One opposition concern is that the agreement allows for continued attacks on the Al Qaeda affiliated Nusra Front - whose militants are widely spread out in opposition-held areas - and other groups designated as terrorists by the UN Security Council.
Opposition fears Russia will use that as a pretext to bomb them.
On Wednesday, Russian President Vladimir Putin held a telephone conversation with King Salman bin Abdulaziz of Saudi Arabia, who is one of the main supporters of the Syrian opposition, to present in detail the proposals that are in a joint US-Russian agreement on a cessation deal in Syria, the Kremlin said.
"The King of Saudi Arabia welcomed the agreements reached and expressed his readiness to work jointly with Russia to make them work," the Kremlin said. The two sides agreed to continue contacts on this matter, it added.
Assad told Putin on Wednesday that his regime was ready to assist in implementing a cessation of hostilities in Syria, the Kremlin and Assad's office said.
Russia has been one of the most important allies of the Assad regime and intervened in the war in Syria starting an air campaign on September 30 last year.
Russian authorities claim to target DAESH and other "terrorist organisations" but an overwhelming majority of Russian air strikes hit opposition forces and residential areas killing hundreds of civilians since the intervention.