NATO is continuing military exercises in the Mediterranean and Adriatic seas amid tensions in eastern Europe over a Russian military buildup near Ukraine’s border.

The Neptune Strike 2022 exercises include a U.S. carrier group led by the USS Truman aircraft carrier, from which F-18 fighter jets flew over the Baltic States, Poland, Romania, and the Ionian Sea.

Italian, Greek, German, and Spanish navies also participated in the drills.

NATO has been bolstering its defenses around allies in Eastern Europe since late last year.

Denmark, for example, said it is sending a frigate and F-16 warplanes to Lithuania, and Spain is sending four fighter jets to Bulgaria and three ships to the Black Sea to join NATO naval forces.

The Netherlands plans to send fighter jets to Bulgaria in April and is putting ship and land-based units on standby for NATO’s Response Force.

The military moves come amid stalled talks with Russia over its buildup at Ukraine’s borders.