SOFIA, July 16 (Xinhua) -- The joint air force drill Thracian Star 2018, involving units from Bulgaria, the United States, Britain and Greece, kicked off in Bulgarian airspace on Monday, officials said.

During the 12-day exercise, U.S. jets F-15 and Royal Air Force Eurofighter Typhoons are to operate from two air bases in neighboring Romania, while the Greek Air Force would fly from its Nea Anchialos Air Base, the statement said.

Bulgarian Air Force would participate with crews and jets MiG-29, Su-25 and L-39 from Graf Ignatievo, Bezmer and Dolna Mitropoliya air bases, as well as with anti-aircraft missile units, it said.

The four NATO allies are performing a wide range of defensive and offensive air missions, it said.

Thracian Star is an annual flying exercise that provide participants with opportunities to generate experience in real interaction in an international environment.