The group published pictures on social media that it said showed the two destroyed two military aircraft parked in front of a hangar.
The Islamist rebel fighters seized Sirte’s military and civilian airport two weeks ago, expanding the area it controls by exploiting a security vacuum in oil-producer Libya, where two governments are vying for power.
The militants had earlier this week seized a power plant in a western suburb of Sirte, completing a gradual takeover of the city that it began in February.
Forces loyal to a self-declared government that controls the capital Tripoli had pulled out of the plant and air base.
Since the start of the year militants in Libya loyal to Islamic State have claimed responsibility for killing dozens of Egyptian and Ethiopian Christians and attacking Tripoli’s luxury Corinthia hotel, embassies and oilfields.
Libya’s internationally recognized government has been working out of the east of the country since losing control of Tripoli and western Libya in August, part of turmoil gripping Libya four years after the ousting of Muammar Gaddafi.