MOSCOW -- Talks between the Syrian government and the opposition ended in acrimony Friday with the parties blaming each other for the breakdown.

The Russian mediator of the weeklong meeting, Vitaly Naumkin, said the parties agreed on a set of principles for a political settlement, including the condemnation of foreign support for terrorist groups, a call for preserving state institutions and lifting economic sanctions.

But some opposition representatives later reversed their support for the initially approved document because of a failure to agree on moves to improve mutual trust, such as prisoners' release, said Naumkin, head of the Moscow-based Institute for Eastern Studies.

"If we spent another week here, we would probably reach agreement on other issues," Naumkin said at a briefing. "They sat at the table together, they didn't go into a fistfight, they listened to each other. It's good."

Moscow arranged the negotiations in a bid to raise its international profile at a time of bitter tensions with the West over Ukraine. The meeting followed the first round of Moscow-hosted talks in January.

"We didn't have any excessive expectations, we didn't expect the meeting to settle the Syrian crisis," Naumkin said, adding that there was no immediate plan for hosting the next round of talks.

The main Western-backed opposition group, the Syrian National Coalition, refused to attend the Moscow talks amid deep distrust of Russia's intentions.

Russia has staunchly backed Syrian President Bashar Assad's government throughout the country's civil war, now in its fifth year, which has killed more than 220,000 people and has turned nearly 4 million into refugees.

Bashar Jaafari, Syria's UN envoy who represented the Syrian government in the negotiations, sought to cast them as a success, hailing the initially agreed document. He tried to downplay opposition reversal of support.

"The government and the opposition managed to reach common ground on a number of important issues," he said at a news conference. Jaafari denied the opposition accusation that the government side was trying to drag out the talks to avoid discussing sensitive issues.

But Samir Aita, one of the opposition representatives who attended the talks, criticized the government for stonewalling demands for prisoner releases. He said "the document doesn't create hope, on the contrary, it destroys it."

The public spat followed Russian Foreign Minister Sergey Lavrov's meeting with negotiators on Thursday, in which he strongly urged the parties to reach a compromise to stem the spread of the Islamic State and other terrorist groups in the region.

"You need to save the country and its people, or there will be no one left to build a renewed, united and sovereign Syria," Lavrov said.

He argued that the U.S.-led air campaign against the Islamic State has failed to reach its goals, and criticized Washington for training some of the rebels, saying it would only fuel the conflict.