SOFIA, May 4 (Xinhua) -- The Bulgaria-United States joint exercise Thracian Eagle 2018, involving a dozen of F-15 jets from the Oregon Air National Guard, kicked off at Graf Ignatievo Air Base on Friday, officials said.

During the five-week drill, the U.S. tactical fighters, together with Bulgarian MiG-29 and L-39 jets and anti-aircraft missile units, would carry out "full range of tasks", Bulgarian Defense Ministry said in a statement.

The main goals of the drill were to achieve greater interoperability of the Bulgarian Air Force for participation in operations under the auspices of NATO, enhance training of the personnel, as well as improve the procedures for logistics and maintenance of visiting formations, the statement said.

U.S. F-16 jets from the Spangdahlem Air Base in Germany would relocate to Graf Ignatievo for three days in the middle of May to join the drill, the statement said.

Joint tasks would also be carried out with British Eurofighter Typhoon fighters and crews of the Romanian Air Force, which would operate from the Mihail Kogalniceanu Air Base in Romania, it added.

The United States and Bulgaria, a NATO member since 2004, signed an agreement in 2006, allowing U.S. troops to be deployed in Bulgaria. Since then, every year the U.S. and Bulgarian soldiers have worked and trained together at the joint training facilities of Graf Ignatievo, Bezmer and Novo Selo.