Syria's main opposition bloc has said it will support a temporary two-week truce to test the seriousness of the other side's commitment to a US-Russian plan to end fighting.
Earlier this week, the US and Russia agreed on a "cessation of hostilities" between the Syrian government and groups fighting it in a deal that excludes the Islamic State of Iraq and the Levant (ISIL) and the al-Nusra Front.
The agreement called on all sides to sign up to the deal by midday on February 26 and to stop fighting by midnight.
"The High Negotiations Committee believes a provisional truce for two weeks would provide a chance to determine the commitment of the other side" to the ceasefire, the opposition bloc said in a statement on Wednesday.
Assad 'ready for ceasefire'
The opposition statement came after Syria's president assured Russia of his readiness to respect the ceasefire, the Kremlin said on Wednesday.
"A phone call took place between Russian President Vladimir Putin and President of the Syrian Arab Republic Bashar al-Assad," the Kremlin said in a statement.
"In particular, [Assad] confirmed the readiness of the Syrian government to facilitate the establishment of a ceasefire."
Assad described the ceasefire as an "important step towards a political resolution" for Syria's civil war, according to the Kremlin statement.
However, Putin and Assad emphasised the need to continue an "uncompromised fight" against ISIL, the al-Nusra Front and other groups "which are included in the respective list of the United Nations Security Council", the Kremlin added.
Putin also discussed the ceasefire with the leaders of Iran and Saudi Arabia on Wednesday.
"Primary attention was focused on the Syrian issues, in particular the discussion of initiatives and proposals laid out in the Joint Statement of Russia and the United States on the cessation of hostilities in Syria," the Kremlin said in reference to Putin's call with Iran's President Hassan Rouhani.
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Saudi Arabia's King Salman bin Abdulaziz al-Saud "welcomed the achieved agreements and expressed readiness for mutual work with Russia to realise them", the Kremlin said.
Saudi Arabia has been a key backer of the Syrian opposition and rebel factions, whereas Russia supports Assad, a longtime ally.
Also speaking on Wednesday, Turkish President Recep Tayyip Erdogan said that he was concerned that the US-Russian plan would provide an advantage for government forces and their backers while being indecisive on the terms for the Syrian opposition.
Erdogan said in a televised address that Turkey welcomed efforts towards a ceasefire in principle, but he accused the US, EU, UN, Iran and Russia of acting dishonourably in Syria by directly or indirectly permitting government forces to kill civilians.
The Syrian government said on Wednesday it was more "determined more than ever" to preserve Syria's unity after US Secretary of State John Kerry said it would be hard to hold the country together if the fighting did not stop.
Damascus was "determined today more than any time to crush terrorism and preserve the unity of Syria", according to a statement published by state media.
Meanwhile, the UN said early on Wednesday that it had made its first airdrop of humanitarian aid to civilians in Syria, delivering 21 tonnes of relief to besieged residents in the eastern city of Deir az-Zor.
"Earlier this morning a WFP [World Food Programme] plane dropped the first cargo of 21 tonnes of items into Deir az-Zor," UN aid chief Stephen O'Brien told the Security Council on Wednesday.
"We have received initial reports ... that pallets have landed in the target area."
Yet WFP later released a statement saying there had been technical difficulties and that they would try the airdrop again in a few days. It is not clear if any aid reached those in need.
UN spokesman Stephane Dujarric also told reporters that the WFP was still trying to get information on where the aid had ended up, suggesting it may not have all reached the target area.
"As you know, airdrops can be very challenging," he said. "The pallets were dropped. They're [the WFP] trying to reach local partners to ensure that the aid was received."
Al Jazeera's James Bays, reporting from the UN headquarters in New York, said the timing of the discussion of aid deliveries was important.
"The idea is not only to help desperate, in some cases, starving people. It is also an important component of the plan drawn up in Munich earlier this month to restart talks between the warring parties in Syria.
"The other part of that plan is the cessation of hostilities which is supposed to come into effect on Saturday."
Source: Al Jazeera and agencies