Throughout the conflict, Russia has been one of Assad's greatest backers, selling him arms and, along with China, protecting Syria from censure by the U.N. Security Council.
But Russian officials have recently distanced themselves from Assad's regime, suggesting they are resigned to his potential ouster.
Also Friday, NATO's top official said that Syria has continued to target rebel areas with Scud-type missiles.
Secretary-General Anders Fogh Rasmusen called the attacks "acts of a desperate regime approaching collapse."
U.S. and NATO officials first reported Syria's use of Scud missiles one week ago, prompting a swift denial from the Syrian government.
NATO agreed earlier this month to deploy Patriot anti-missile systems along Syria's northern border with Turkey — a move Fogh Rasmussen said was justified by the new attacks.
One of the Scuds apparently hit the rebel town of Marea, near Aleppo.
An activist in the town who goes by the name Abu al-Hassan said Friday he was awoken the day before by the largest explosion he'd ever heard in the town, a frequent target of regime airstrikes.
"It shook the house and my kids came running in saying, 'Daddy, daddy!'" he said. "They were terrified."
Al-Hassan said the missile fell in a field, causing no casualties.
Videos purporting to show the impact site showed a crater some six meters (yards) deep in a green field. They appeared genuine and corresponded with other AP reporting on the incident.
Also Friday, a prominent news anchor from Syrian state TV said he had defected after being repeatedly interrogated by the country's intelligence services.
Speaking from an undisclosed location outside of Syria, Ahmad Fakhouri told Al-Arabiya TV that he'd fled the country eight months ago with rebel help.
"I look forward for the day when Syria will be free and I can return to my country to do my job," he said.
Syrian TV's head office in Damascus told The Associated Press that Fakhouri had left the station to work for state-run radio.
An official at the radio station said Fakhouri was on vacation.
Associated Press writers Bassem Mroue in Beirut and Vladimir Isachenkov in Brussels contributed reporting.
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