The UN has suspended peace talks aimed at ending Syria's five-year civil war, just days after they began.
But the organisation's special envoy, Staffan de Mistura, insisted negotiations had not failed, and would resume on 25 February.
Each side blamed the other for the collapse of the round.
It came as the Syrian government said it had dealt a major blow to the opposition by cutting a key supply route to the rebel-held city of Aleppo.
Syrian state television reported that government forces had broken the siege of Nubul and Zahraa, two towns north-west of Aleppo.
On the talks, Mr de Mistura admitted that "there's more work to be done".
"It is not the end and it is not the failure of the talks," he said.
"They came and they stayed. Both sides insisted on the fact that they are interested in having a political process started."
Syrian government delegation head Bashar Jaafari blamed the opposition for the suspension.
Mr Jaafari accused them of acting under the orders of Saudi Arabia, Qatar and Turkey "to bring about the talks' failure", Syrian state television reported.
Blaming the government for the failure, Syria's opposition High Negotiations Committee (HNC) said they would not return until conditions improved on the ground.
"The whole world sees who is making the negotiations fail. Who is bombing civilians and starving people to death," HNC chief co-ordinator Riad Hijab said.
The opposition has been angered that government offensives backed by Russian airpower have continued as talks got under way.
The US said Russia was partly to blame for the suspension, saying its air strikes were deliberately targeting opposition groups.
"It is difficult in the extreme to see how strikes against civilian targets contribute in any way to the peace process now being explored," state department spokesman John Kirby said.
France accused the Syrian government and Russia of "torpedoing" the peace talks with its military action.
But earlier, Russian Foreign Minister Sergei Lavrov stressed that it would not stop the air strikes "until we really defeat terrorist organisations like al-Nusra Front".
More than 250,000 people have died in almost five years of war in Syria.
Eleven million others have fled their homes as forces loyal to President Bashar al-Assad and those opposed to his rule battle each other, as well as the Islamic State group.
A donors' conference opens in London on Thursday aiming to raise billions in new funding for those affected.