The activists say rebels from the al-Qaida affiliated Jabhat al-Nusra and other Islamic groups seized control of buildings, ammunition and military equipment in the sprawling Taftanaz air base in northern Idlib province Friday.
Taftanaz is the biggest field in the country's north for helicopters used to bomb rebel-held areas and deliver supplies to government troops.
Idlib-based activist Mohammad Kanaan said the fighters took control Friday morning after several days of intense fighting.
Rami Abdul-Rahman, director of the Britain-based Syrian Observatory for Human Rights said it is the first major military airport to fall into rebel hands.
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