"If the United States ... recognizes one of the key Syrian opposition organizations, al-Nusra, as terrorist ... how can one deliver arms to those opposition members? Where will they end up? What role will they play?” asked Russian President Vladimir Putin during a joint news conference with German Chancellor Angela Merkel on Friday.

"Assad goes today, a political vacuum emerges - who will fill it? Maybe these terrorist organizations," Putin said. "Nobody wants this - but how can it be avoided? After all, they are armed and aggressive."

"We are concerned about the possible appearance of a political vacuum in Syria if some decisions about a change of government in Syria are taken now," he said.

Putin said the only answer was an international peace conference that Russia and the United States want to convene.

"There is only one reasonable idea, which everybody supported at the G8," he said, referring to a summit this week in Northern Ireland.

"It is to force all conflicting sides to come to Geneva ... and sit at the negotiating table, stop the violence, and find acceptable forms for the future structure of their state and the provision of security for all ethnic and religious groups."

He repeated Russia's position that Mr. Assad's fate and Syria political future should not be decided by outsiders.

"Should Assad stay, should he go, what forms of political leadership should emerge, what constructs - you and I should not impose these things on the Syrian people from abroad," Putin said.

He told a reporter who repeated some media propaganda that Mr. Assad was using weapons against his own people, Putin said "It is not the Syrian people that are fighting against Assad, but militants, well trained and armed," Putin said.

US President Barack Obama decided a week ago to provide military aid to militants trying to overthrow Mr. Assad who enjoys a considerable popular support among Syrian people.