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Pavel Golovkin, Associated Press
Qadri Jamil, left, former deputy prime minister representing Syria's opposition Popular Front of Change and Liberation, Samir Aita, center, a member of Syrian Democratic Forum, and Suleiman Numrud, an independent Syrian opposition member, attend a news conference in Moscow, Russia, Friday, April 10, 2015. Representatives of the Syrian government and opposition have wrapped up four days of talks in Moscow, with an opposition leader calling for a third U.N.-sponsored international conference aimed at resolving Syria’s four-year civil war.

MOSCOW — Talks between the Syrian government and the opposition ended in acrimony Friday with the parties failing to bridge their differences.

The Russian mediator of the weeklong meeting, Vitaly Naumkin, said the parties agreed on a set of principles for a political settlement, but acknowledged that they couldn't reach accord on confidence-building measures.

Some of the participants later reversed their support for the initial set of principles because of a failure to agree on steps to release prisoners and other moves to improve mutual trust, Naumkin said.

"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.

"We didn't have any excessive expectations, we didn't expect the meeting to settle the Syrian crisis," Naumkin said.

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

Lavrov said the U.S.-led air campaign against the Islamic State has failed to reach its goals, and he criticized Washington for training some of the rebels.

The main Syrian opposition group refused to attend the talks in Moscow, which followed a first round of negotiations in January.

Russia has staunchly backed Syrian President Bashar Assad's government throughout the country's four-year civil war, shielding it from United Nations sanctions.