By Barbara Starr
Ukrainian military forces have moved into defensive positions around bases and weapons depots in the past few hours, according to a U.S. defense official familiar with the latest intelligence.
The move is seen by the United States as an effort to ensure the military's facilities remain secure.
So far, the move appears to mainly involve Ukraine military personnel, with no widespread movement of armored vehicles.
All of that is leading to the preliminary U.S. assessment that the move is defensive.
By Barbara Starr, Evan Perez and Greg Botelho, CNN
In two operations in Africa nearly 3,000 miles apart, U.S. military forces went after two high-value targets over the weekend.
One operation took place early Saturday in the Libyan capital of Tripoli, when U.S. forces captured Abu Anas al Libi, an al Qaeda leader wanted for his role in the deadly 1998 bombings of two U.S. embassies in Africa.
In the second raid, a team of U.S. Navy SEALs in southern Somalia targeted the top leader of Al-Shabaab, a terrorist group linked with al Qaeda.