The Pentagon said on Friday it would keep a US aircraft carrier battle group in the Mediterranean Sea for several days longer than planned as part of the effort to reassure US allies worried about the crisis in Ukraine.

Army Colonel Steven Warren, a Pentagon spokesman, said the carrier USS George H.W. Bush and its accompanying warships would remain in the region for "a few more days to do additional training and to enhance maritime capabilities."

"This is a few more days over what the original plan was," Warren said. "There's two reasons. One is to conduct these additional training opportunities, and frankly because a lot of what we're doing there now is an effort to reassure our allies."

Warren did not rule out the Bush remaining even longer in the Mediterranean, but said: "Right now she's scheduled to continue on her mission within the next couple of days."

The Pentagon has taken a number of steps to reassure allies over the crisis in Ukraine, which says Russian forces have occupied its Crimean peninsula, where Russia's Black Sea fleet is based. Washington has bolstered its training with Poland's air force and will provide more aircraft for the NATO air policing mission in the Baltics.

Warren said six of the 12 F-16s ordered to Poland arrived on Thursday and the remaining six would arrive on Friday. A C-130 and a C-17 transport planes were due to land in Poland on Friday with supplies and 150 personnel for the training mission, which is due to begin next week once maintenance teams have arrived.

US officials said on Thursday that Ukraine had requested American military assistance, both lethal and non-lethal. The officials, who spoke on condition of anonymity because of the sensitivity of the situation, said Washington had agreed to send military food rations but was weighing other requests, including lethal aid. "I can confirm Ukraine has submitted to the State Department a request for equipment," Warren said. "We are reviewing that request now. Portions of that request have been filled and we're continuing to review the rest of it."
Warren said the United States aimed to deliver 25,000 cases of military rations to Ukraine.