KIEV, Ukraine — Ukraine’s president has gone aboard a U.S. warship making a call at a Ukrainian port, hailing its visit as a warning to Russia.

President Petro Poroshenko visited the destroyer USS Donald Cook in the port of Odessa on Tuesday. He said in a statement that the ship’s visit was “an important signal to the Kremlin,” underlining close U.S.-Ukrainian military cooperation.

Poroshenko also met with Kurt Volker, the U.S. special envoy on Ukraine, thanking the U.S. for expanding its presence in the Black Sea after the Russian seizure of three Ukrainian vessels and their crews in November. The incident further escalated the tug-of-war that followed Russia’s 2014 annexation of Ukraine’s Crimean Peninsula.

Volker described the destroyer’s visit as “a strong symbol of the United States’ commitment to the people of Ukraine.”