The United States sought to keep alive a ceasefire in Syria's civil war on Tuesday as other countries voiced skepticism that a US-Russian deal to halt the violence could be revived.
Senior officials from 23 nations emerged from a one-hour meeting on Syria with little more than an agreement to meet again, on Friday, about how to end a conflict that has killed hundreds of thousands of people in 5-1/2 years.
They also offered differing views over renewing a ceasefire shattered by a strike on a humanitarian aid convoy on Monday, with France's foreign minister saying talks between the United States and Russia seemed close to the end of the road.
The United States and Russia are on opposite sides of the war, with Moscow backing Syrian President Bashar al-Assad and Washington supporting rebels seeking to topple him. Both countries share a commitment to defeat Islamic State militants who control parts of Syria and neighboring Iraq.
"The ceasefire is not dead," US Secretary of State John Kerry told reporters as he came out of the gathering of the International Syria Support Group with Russian Foreign Minister Sergei Lavrov, a meeting that took place on the sidelines of the annual United Nations General Assembly.
French Foreign Minister Jean-Marc Ayrault voiced doubts.
"Is there still a chance this ceasefire will be effective? I can't answer that question," Ayrault told reporters. He said that without a ceasefire there would be a "spiral of war, but we have to be honest, the U.S.-Russian negotiation has reached its limits."
Syria's chief opposition coordinator Riad Hijab told Reuters in an interview that international efforts to achieve a ceasefire were doomed without any credible mechanism to designate blame or attribute consequences.
Hijab said the opposition had information proving Russia and Syria were behind the attack on the UN convoy.
"We have no faith in the Russian side because their strategy is purely military." Hijab said.
US President Barack Obama, who has sought to avoid his country becoming entangled in another Middle East war, said that the only way to end the conflict was through diplomacy, not force, and gave no hint as to what fresh steps Washington might take.
"In a place like Syria where there's no ultimate military victory to be won, we're going to have to pursue the hard work of diplomacy that aims to stop the violence and deliver aid to those in need and support those who pursue a political settlement," Obama said in his speech to the UN gathering of world leaders.
The United Nations suspended all aid shipments into Syria after Monday's deadly attack on a convoy carrying humanitarian supplies to a town near Aleppo, as a week-old U.S.-Russian sponsored ceasefire collapsed in renewed violence.
The Syrian Red Crescent said the head of one of its local offices and about 20 civilians were killed in the strike, which a war monitoring group blamed on Russian or Syrian aircraft.
The Russia and Syrian militaries denied involvement and the Russian defense ministry said it had studied video taken by activists on the ground and found no evidence the convoy was struck, suggesting some damage was caused by fire.
The US military, however, said it believed air strikes had taken place and it denied aircraft from a US-led coalition were flying in the area. It said the only other planes flying over Syria were from Russia and the government of Syria itself.