The U.S. Navy’s guided-missile destroyer Donald Cook re-entered the Black Sea Tuesday to conduct exercises with Ukraine and other allies, the Navy announced Tuesday.

The ship’s arrival in the Black Sea — its second visit this year — comes amid escalating tensions and violence between Russian-backed separatists and Ukrainian forces. The Ukrainian navy has been drilling in anticipation of an attack by sea by Russian forces, particularly near the Ukrainian port of Mariupol, where Moscow seized and imprisoned 24 sailors on three Ukrainian vessels late last year.

During the deployment, the Arleigh Burke-class Donald Cook will make a visit to the Ukrainian port of Odessa, according to Adm. James Foggo, commander of Naval Forces-Europe.

“Russian activity in the last year has become progressively more aggressive and restrictive,” particularly regarding access to Mariupol, Foggo said. “They’ve done it on purpose. It’s economic strangulation.”

The sailors are still imprisoned, which “irritates me to no end,” Foggo said. “They are uniformed sailors.”

The Donald Cook will conduct “maritime security operations and enhance regional maritime stability, combined readiness and naval capability with our NATO allies and partners in the region,” the Navy said.