MOSCOW: Russia has not discussed the possibility of taking in Syrian President Bashar al-Assad, a senior aide to President Vladimir Putin said on Thursday.

Foreign policy adviser Yuri Ushakov's remarks appeared aimed to display indifference about the fate of Assad, whom Moscow has protected from Western pressure, but he gave no sign Russia would shift its stance and support a sanctions threat.

Putin had not discussed where Assad might go if he left Syria either in talks with Turkish Prime Minister Tayyip Erdogan or in a telephone conversation with U.S. President Barack Obama on Wednesday, Ushakov said.

Asked whether Assad could come to Russia, Ushakov said: "I don't know; at least I have not heard about this."

Assad has made no public appearance or statement since a bomb in Damascus killed his powerful brother-in-law, his defence minister and a top general on Wednesday, an attack that prompted government forces to rain artillery fire on rebels.

An official source said Assad was in Damascus, but opposition sources and a Western diplomat said Assad was in the coastal city of Latakia, directing the response to the assassinations, while Damascus residents reported the heaviest fighting in the capital in the 16-month revolt.

The pressure on Assad, engaged in what Russia's foreign minister called a "decisive battle", has prompted speculation that he could seek refuge abroad - possibly in Russia, which has blocked Western efforts to oust him.

Moscow says it is not propping up Assad but that his exit from power could only come as the result of an internal political dialogue and must not be a precondition to such talks.

Ushakov made clear Russia and the United States still disagreed on how to resolve the conflict.

"One can say that Putin and (U.S. President Barack) Obama understand the position of the other side better. As for practical paths to resolving the situation, differences remained," he said.

The United States, Britain, France and Germany, have proposed a U.N. Security Council resolution that would threaten Assad and his government with sanctions in a bid to halt the violence. Russia has put forward it own resolution which does not contain a sanctions threat.

In Putin's conversation with Obama, the Russian leader "was unable to convince" the United States, Ushakov said.

The White House said Putin and Obama agreed on the need to stop the violence but differed over the way forward.

"They noted the differences our governments have had on Syria, but agreed to have their teams continue to work toward a solution," the White House said in a statement.