The U.S. Navy began its bilateral passing exercise known as PASSEX with ships from the Romanian, Turkish, and Ukrainian Navies on Sunday.

PASSEX is conducted to improve the maritime capabilities between the U.S. Navy and other naval forces involved. The training event comes as Ukrainian armed forces continue their fight against Moscow-supported militants in the eastern part of the country, and political tensions escalate between Turkey and Russia. The commanding officer of the Arleigh Burke-class guided-missile destroyer USS Ross says the event helps improve ties between the naval forces.

"I was very happy to support this recent PASSEX with our allies and partners," Cmdr. Russel Caldwell said in a statement. "Operating in the Black Sea and working with our allies provides us with an excellent opportunity to strengthen and reaffirm our partnerships. I look forward to future PASSEX opportunities with partner nations in these waters."

PASSEX included advanced ship maneuvering, search and seizure training, and air defense exercises.

USS Ross operates as part of the U.S. Navy's 6th Fleet of responsibility, which regularly conducts naval exercises and patrol missions in the Mediterranean Sea to support both the U.S.'s national security interests and stability in Europe and Africa.

The 6th Fleet is headquartered in Naples, Italy.