The astronaut, Mohammad Ahmad Faris, joins a long list of high-profile defectors to the rebel Free Syrian Army.
Syria's first man in space has fled to Turkey and joined opposition forces fighting President Bashar Assad's regime, the latest in a string of high-ranking defections from the conflict-stricken country, Turkey's state-run news agency reported Sunday.
Mohammad Ahmad Faris, 61, crossed into Turkey after reaching the headquarters of the Free Syrian Army in Aleppo, meeting with rebel commanders there, and declaring his solidarity with the umbrella group of rebel fighters, the Anadolu agency reported.
"We are with you with our lives and blood," Anadolu quoted Faris as telling members of the Free Syrian Army.
The agency said Faris crossed into Turkey on Sunday, but Mahmut Osman, an Istanbul-based member of the Syrian opposition group — the Syrian National Council — said he had arrived in Turkey on Saturday and would hold a news conference in Istanbul in the coming days. He would not disclose Faris' current whereabouts.
Anadolu reported that it was Faris' fourth attempt to defect, after three previous efforts had failed. It gave no details on his escape and provided no source for the report.
Faris joins a string of high-profile figures, including senior army officers, who have abandoned Assad's regime since the uprising began in March 2011. Last month, Brig. Gen. Manaf Tlass, an Assad confidant and longtime friend, became the first member of his inner circle to defect in a move hailed as a triumph by the opposition. In July, a member of Syria's parliament also fled denouncing the violence by Assad's regime.
Faris, an air force pilot, was part of the three-man crew of a Soviet space mission in 1987 and Syria's first man in space, Anadolu reported.
Aleppo, Syria's largest city, is close to the Turkish border and is where the rebels have their rear bases. Armed government troops have been steadily shelling rebel-controlled parts of the city.
Turkey has some 45,000 refugees in camps along the 911-kilometer (566-mile) border and is also a staging ground for the Free Syrian Army rebels.