The Netherlands has deployed four F-35 combat aircraft to Bulgaria to help carry out air patrol missions amid the Ukraine crisis, the Defense Ministry said, Reuters reported.

Dutch warplanes, along with Bulgarian MiG-29 fighter jets, will help protect the airspace of the Black Sea country until May 31 in accordance with NATO's comprehensive air and missile defense plan.

They will replace the four Spanish fighter jets that have been monitoring Bulgarian airspace since mid-February.

Bulgaria, located on NATO's eastern flank, is also building a battle group of up to 1,000 troops in close cooperation with the alliance.