Unidentified armed men fired in the air as they moved into a Ukrainian naval post in Crimea on Monday in the latest confrontation since Russian military groups seized control of the Black Sea peninsula.
In other armed action, Russian forces took over a military hospital and a missile unit. Reuters correspondents also saw a big Russian convoy on the move just outside the port city of Sevastopol near a Ukrainian air defense base.
It comprised more than 100 vehicles, including around 20 armored personnel carriers, plus mobile artillery.
With diplomacy at a standstill, Russia said the United States had spurned an invitation to hold new talks on resolving the crisis, the worst East-West standoff since the Cold War.
Ukrainian Prime Minister Arseny Yatseniuk, who said he would address the U.N. Security Council on Thursday, put the blame for the crisis on Russia and accused Moscow of undermining the global security system by taking control of Crimea.
Russian forces have in little more than a week taken over military installations across Crimea, home to the Russian Black Sea Fleet and Russian territory until Soviet leader Nikita Khrushchev gave it to Ukraine in 1954.
Pro-Russian separatists have taken control of the regional parliament, declared Crimea part of the Russian Federation and announced a referendum for Sunday to confirm this.