Syria's government and the opposition have blamed each other for the suspension of peace talks in Geneva.
UN envoy Staffan de Mistura called a temporary pause, saying the talks would resume on 25 February.
But the opposition HNC said they would not return until conditions improved on the ground, accusing government forces of bombing and starving civilians.
The government said the opposition caused the suspension, acting on the orders of Turkey and Gulf states.
On Thursday a donor's meeting takes place in London aiming to secure extra funding for those affected by the war.
Over 70 countries are taking part, with the UN hoping to raise billions of dollars. Funding last year fell 60% short of the UN's target.
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.
The civil war has also been a major driving force behind Europe's migration crisis.
Announcing the suspension of the talks, Mr de Mistura admitted "there's more work to be done".
But he said "it is not the end and it is not the failure of the talks".
The opposition High Negotiations Committee (HNC), however, soon cast doubts over whether they would return.
"The whole world sees who is making the negotiations fail. Who is bombing civilians and starving people to death," the HNC's chief coordinator Riad Hijab said.
The Syrian government said the talks' suspension was down to the opposition.
The head of the Syrian delegation, Bashar Jaafari, accused them of acting under the orders of Saudi Arabia, Qatar and Turkey "to bring about the talks' failure", Syrian state television reported.
Analysis: BBC's Imogen Foulkes in Geneva
It was always known these talks would be difficult, but no-one expected them to end after just two days, with the UN special envoy standing in the driving sleet outside the opposition's Geneva hotel to deliver the news.
Staffan de Mistura insists this is a temporary pause, not failure. But these negotiations never really got started. Hardly any of the planned meetings with UN negotiators actually happened, the two sides were never even in the UN at the same time, let alone in the same room.
Their conditions for engaging in negotiations were poles apart: the opposition wanted sieges lifted and prisoners released, the Syrian government played for time, asking for a written agenda and a full list of participants.
Meanwhile, on the ground, the war rages on, with the Syrian army, backed by Russian bombing, retaking rebel-held territory. The UN says the peace talks will start again on 25 February, but if the military push continues, things in Syria could look very different by then.
Meanwhile France accused the Syrian government and Russia, who has been carrying out air strikes in support of President Assad, of "torpedoing" the peace talks.
French Foreign Minister Laurent Fabius said Moscow and Damascus "visibly don't want to contribute to them in good faith".
The US also said Russia was partly to blame for the suspension, saying its air strikes were deliberately targeting opposition groups.
In a strongly worded statement, Secretary of State John Kerry said that "the continued assault by Syrian regime forces - enabled by Russian air strikes - against opposition-held areas... have clearly signalled the intention to seek a military solution rather than enable a political one".
Both the US and France have condemned Russian bombing around Syria's second city of Aleppo, and Mr Kerry repeated his demand for the bombardment to stop.
"It is past time for them to meet existing obligations and restore the international community's confidence in their intentions of supporting a peaceful resolution to the Syrian crisis," Mr Kerry said.
"During this pause [in the talks], the world needs to push in one direction - toward stopping the oppression and suffering of the Syrian people and ending, not prolonging, this conflict."
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".
Syria's opposition has been angered that major government offensives continued as the talks got under way.
On Wednesday, the government claimed a major victory against the rebels by breaking a siege of two towns north-west of the city of Aleppo, severing a key rebel supply route into the city.
Syria conflict - key questions
Why is there a war in Syria?
Anti-government protests developed into a civil war that, four years on, has ground to a stalemate, with the Assad government, Islamic State, an array of Syrian rebels and Kurdish fighters all holding territory.
Who is fighting whom?
Government forces concentrated in Damascus and the centre and west of Syria are fighting the jihadists of Islamic State and al-Nusra Front, as well as less numerous so-called "moderate" rebel groups, who are strongest in the north and east. These groups are also battling each other.
How has the world reacted?
Iran, Russia and Lebanon's Hezbollah movement are propping up the Alawite-led Assad government, while Turkey, Saudi Arabia and Qatar back the more moderate Sunni-dominated opposition, along with the US, UK and France. Hezbollah and Iran are believed to have troops and officers on the ground, while a Western-led coalition and Russia are carrying out air strikes.