(Adds comment by senior U.S. defense official)
By David Alexander
WASHINGTON, April 2 (Reuters) - The Pentagon said on Wednesday it was bolstering the size of its Europe-based African crisis response force to 675 Marines, sending 175 new troops to a Romanian base near the Black Sea at a time of tensions over Russia's annexation of part of Ukraine.
The Marines will be part of a team headquartered in Moron, Spain, and primarily meant for operations in Africa, although they can be sent anywhere, a Pentagon spokesman said. The decision to base the additional Marines in Romania was made last year before the current crisis, he said.
But it came on the heels of news on Tuesday that General Philip Breedlove, the top U.S. officer in Europe, is considering moving a U.S. warship into the Black Sea in the coming days to reassure NATO allies and exercise with partners.
Army Colonel Steve Warren, a Pentagon spokesman, confirmed the department was looking at sending a ship to the Black Sea. He did not rule out exercises with the Ukrainian navy, but added the ship's schedule of activities was still being decided.
"This is to reassure our allies of our commitment to the region. ... It is a direct result of the current situation in Ukraine," Warren told reporters.
Elaine Bunn, deputy assistant defense secretary for nuclear and missile defense policy, told a Senate subcommittee hearing that U.S. officials were in close touch with European allies in NATO about possible "military options for strengthening the collective defense." She declined to give details.
Warren said the decision to send 175 Marines to Mihail Kogalniceanu military base in Romania, near the Black Sea port of Constanta, was made before Russia seized control of Ukraine's Crimean peninsula last month.
Some 265 Marines are already stationed at the Romanian base as part of a Black Sea Rotational Force that conducts training and other efforts to help build the military capacity of partners in the region.
Other U.S. forces also are stationed at the Romanian base, which is taking over as a transit hub for equipment being flown in and out of Afghanistan following the decision to close the transit center at Manas in Kyrgyzstan this summer.
To accommodate the additional Marines, U.S. officials in Romania sought and received permission from the government to have up to 600 Marines in the country at any given time, Warren said.
He said the intent was to maintain the Black Sea Rotational Force of about 300 Marines, and 175 Marines for the crisis response force, plus some "head room" for additional personnel when troops who are rotating into the country overlap with those departing. The Black Sea Force is due to rotate soon, he said.
The 175 additional Marines being sent to Romania will be coming from Camp Lejeune in North Carolina and will be attached to the Special Purpose Marine Air-Ground Task Force - Crisis Response, which was created following the attack on the U.S. consulate in Benghazi, Libya.
"This ... is frankly not linked to the current situation in Ukraine," Warren said. "They belong to Africom (U.S. Africa Command) and the purpose of them is to be able to respond to crises, really throughout the region."
The new Marines will expand the size of the crisis response force to 675 from 500. (Additional reporting by Andrea Shalal; Editing by Eric Walsh and Mohammad Zargham)