The United States and France have charged Russia and the Syrian regime with stymieing peace negotiations with an unrelenting campaign to retake opposition-held territory even during the talks.
Throughout two days of fitful negotiations in Geneva on February 1 and 2, Syrian ground forces backed by Russian air strikes were waging an intense campaign to retake rebel-held territory around the strategic city of Aleppo in Syria's north, and on February 3 they succeeded in cutting off the rebels' supply line from Turkey.
The campaign, undeterred by the talks, was cited as the reason that the largest opposition coalition refused to fully join the negotiations, and "military activities" were also cited by United Nations Syrian envoy Staffan de Mistura as a principle reason for suspending the negotiations on February 3.
French Foreign Minister Laurent Fabius accused the Syrian government and its allies of "torpedoing" the peace talks and said "neither [Syrian President] Bashar al-Assad's regime nor his allies clearly want to contribute in good faith" to the negotiations.
"We condemn the Syrian regime's brutal offensive with support from Russia to surround and suffocate Aleppo and its hundreds of thousands of residents," he said.
U.S. State Department spokesman John Kirby said the Russian air strikes around Aleppo have almost exclusively targeted opposition groups represented at the peace talks rather than Islamic State or Al-Nusra militants that both sides are fighting, and thus were partly responsible for forcing a suspension of the peace talks.
The air strikes have prompted reports of more civilian casualties, displacement of Syrian citizens, and the obstruction of humanitarian aid shipments, he said.
"It is difficult in the extreme to see how strikes against civilian targets contribute in any way to the peace process now being explored," he said.
U.S. Secretary of State John Kerry late on February 3 released a statement saying the Russian air strikes and continued attacks by Syrian government forces signaled their intention to pursue a military rather than a political solution to the Syrian conflict.
Kerry called on Russia and Syria to halt their bombardment of opposition-held areas, especially Aleppo, and end sieges of civilians, as required by a UN resolution, to allow the resumption of the peace negotiations.
"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," Kerry said.
While UN envoy de Mistura did not specifically cite the fighting around Aleppo, a senior aide told Reuters that he suspended the negotiations until February 25 "because the organization did not want to be associated with the Russian escalation in Syria, which risks undermining the talks completely."
"The stepped up air strikes gain the government ground, but also aim at humiliating the opposition on the ground and in Geneva," the aide said.
Russia and Syria denied causing what is being billed as a temporary break-up of the negotiations but which could prove to be their dissolution.
The head of the Syrian government delegation in Geneva, Bashar Ja'afari, blamed the break-up on "a failure of everybody except the government of the Syrian Arab Republic."
He said opposition groups were preparing to walk away from the talks because they were losing the fight on the ground, and the UN moved to suspend the talks to cover up that fact.
Russian Deputy Foreign Minister Gennady Gatilov blamed opposition groups for demanding an end to the fighting and the delivery of humanitarian aid to besieged towns as "preconditions" to joining the talks.
"Their attempts to frustrate the negotiating process under an excuse that Russia continues its military operation in Syria are absolutely unacceptable," Gatilov said, insisting that Russia was bombing only "terrorists."
"We have repeatedly said that antiterrorism efforts are a matter of top priority for us and for the Syrian authorities," he said.
Gatilov added that when the negotiations resume, they should include opposition groups that were excluded previously, such as the Syrian Kurds, who hold large swathes of Syrian territory in the north.
Opposition groups said they would not return to the negotiations until the fighting stopped and humanitarian aid was delivered to starving residents of besieged towns.
"We are waiting for the United States to stop leading from the back, and the Russians...to stop adding fuel to the fire," opposition spokeswoman Farah al-Atassi said.