Syria's foreign minister has raised the prospect of a ceasefire in the city of Aleppo in a move that could see the government and opposition agree to a prisoner exchange.

Foreign minister Walid Moualem raised the plan with Russia's foreign minister Sergei Lavrov ahead of the planned Geneva II conference on Syria next week in Switzerland.

"Today, I submitted to Minister Lavrov a plan for security arrangements that have to do with the city of Aleppo," he said.

"I asked him to make necessary arrangements to guarantee its implementation and to specify the zero hour for military operations to cease."

The Syrian government says it will attend the conference but the fractured opposition has not yet given a commitment.

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Members of the Syrian National Coalition, the main opposition group, are meeting in Turkey to discuss the issue but several dozen have walked away from talks over differences of opinion on the future of president Bashar al-Assad.

"We refuse most of the policies now inside the coalition. Most of them doesn't reflect the attitude of the revolutionists inside Syria. So for that, we are out of these meetings now," coalition member Khaled Ali said.

Aleppo, in the country's north, has been a flashpoint in the country's three-year civil war and the scene of some of the most brutal violence in the conflict.