MOSCOW -- A Syrian opposition leader has called on the Kremlin "not to send controversial messages" that support President Bashar Assad regime's violent crackdown on popular protests.

Moscow remains one of the few supporters of Assad's government after an 8-month-old uprising that left at least 3,500 dead. Russia and China have also vetoed a European-backed U.N. Security Council resolution on Syria that aimed to impose sanctions on Damascus.

The head of the opposition Syrian National Council, Burhan Ghalioun, said Tuesday that Russia's support "plays a very negative role" in Syria.

Ghalioun's Council has pledged to forge a united front against Assad. He visited Moscow for talks with Russian senators and diplomats.

Syria has been one of Russia's key Mideast allies since the Soviet era.