CONSTANTA, Romania (AP) — The U.S. Air Force on Monday flew in two F-22 Raptor fighter jets to Romania as a show of strength to deter Russian intervention in Ukraine.

The fighter jets landed at the Mihail Kogalniceanu air base, near the Black Sea port of Constanta in southeast Romania. A U.S. statement says they possess sophisticated sensors allowing the pilot to track, identify, shoot and kill air-to-air threats before being detected. The fighters also have a significant capability to attack surface targets.

Russia-backed separatists have been fighting government troops in Ukraine since April 2014, leaving at least 9,100 dead. The conflict has left many neighboring countries in Central and Eastern Europe jittery about Russia's intentions in the region.

U.S. Ambassador Hans G. Klemm said the U.S. and Romania, a NATO member since 2004 that has a population of 19 million, were seeking to improve "the defense of Europe, the defense of the North-Atlantic Alliance, to improve the security in South Eastern-Europe ... as a result of the aggression by Russia that has brought so much instability to this part of the world over the past two to three years."

Romanian Air Force chief of staff Maj. Gen. Laurian Anastasof voiced concerns about Russia's presence in the region. He said that if a Russian plane took off from an air base in Crimea and went 100 kilometers (62 miles) beyond Crimea's borders "that can trigger worries of the (NATO) alliance."

Anastasof said that if an unidentified aircraft comes within 20 miles (32 kilometers) of Romania's airspace, NATO'S procedure "obliges us to scramble planes up in the air, a scenario that had already happened four times this year." He said no Russian plane had come close to Romania's airspace.

The U.S. fighter jets, which arrived from Britain, will leave Romania later Monday. They are part of the Operation Atlantic Resolve, a U.S. commitment to NATO's collective security and regional stability.