Jan. 28 (UPI) -- The Navy destroyer USS Porter entered the Black Sea Thursday to conduct routine maritime security operations with NATO allies and partners in the region.
Guided missile destroyer USS Donald Cook and replenishment oiler USNS Laramie arrived Sunday.
"The Black Sea is of strategic importance to NATO. Three Allies -- Bulgaria, Romania and Turkey -- are littoral states, while Georgia and Ukraine are close partners," NATO spokesperson Oana Lungescu said.
"In response to Russia's illegal and illegitimate annexation of Crimea from Ukraine and its ongoing military build-up in the Black Sea, the Alliance has increased its defensive presence in the region and remains strongly committed to Black Sea security," Lungescu said.
The U.S. Navy and other NATO navies typically patrol waters in the Black Sea about two-thirds of the year, according to NATO.
NATO also announced Thursday that the Spanish Air Force has deployed six fighter aircraft to Romania for air policing.
The Spanish aircraft are stationed at Kogalniceanu airbase on Romania's Black Sea coast and will fly alongside the Romanian Air Force.