The countries also reiterated “their determination to fight jointly” against the Islamic State and against Al Qaeda’s affiliate in Syria, formerly known as the Nusra Front, pledging to “separate” them from armed opposition groups. That could be an important provision, since the Syrian government led by President Bashar al-Assad tends to classify all the opposition fighters indiscriminately as terrorist groups, and many have been unable or unwilling to separate themselves from forces of the former Nusra Front on the battlefield.

The agreement did not specify how such a separation might occur, however.

In Astana, government representatives said that they still considered the rebel fighters to be terrorists and were waiting to see if Turkey followed through on the agreement. Rebel negotiators said the meetings had given them hope that Russia might be open to hearing rebel concerns and become more willing to press the Syrian government for a political resolution, but such optimism did not extend to Iran, which had stuck to a harder line.

Staffan de Mistura, the special United Nations envoy for Syria who had been invited to the Astana talks, said in an interview after the joint statement was issued that in the interactions he had watched between Russia and opposition commanders, “The body language was of people who were seriously talking to each other and taking each other seriously.”

At the same time, rebels are concerned that the new agreement puts Iran in the position of taking part in a cease-fire that its own militias have been accused of violating.

The next round of talks between the Syrian government and the opposition will occur on Feb. 8 in Geneva, according to the announcement by the three countries. But diplomats in Astana said it was unclear if that date was firm.

Bashar al-Jaafari, the Syrian ambassador to the United Nations who led his government’s delegation to the talks in Astana, said an offensive by the government and its allied troops would continue, arguing that Qaeda-linked “terrorist groups” controlled Ain al-Fijeh, a town in Wadi Barada. Residents in Wadi Barada say that some fighters from the former Nusra Front are present there, but that they are at most a tiny minority.