Russian troops have stormed a Ukrainian airbase in Crimea throwing stun grenades and firing automatic weapons in the air.
Reports say at least one person was injured during the assault on Belbek base, near Sevastopol. The base is now said to be under Russian control.
Earlier, several hundred unarmed protesters seized a Ukrainian naval base at Novofedorivka, western Crimea.
Russia formally annexed the Ukrainian region on Friday.
Russian forces appear to be stepping up their efforts to push all Ukrainian forces out of the region.
In another development, Ukraine's warship Slavutych has been seized.
The command vessel was seized by Crimean "self-defence" units and Russian troops after a two-hour assault in Sevastopol, a Ukrainian defence spokesman said.
The BBC's Ian Pannell in Belbek says the Ukrainian troops on the peninsula feel beleaguered and abandoned by their commanders.
In Belbek, two armoured vehicles burst through the wall of the base followed by Russian troops firing weapons in the air.
An ambulance was then seen entering the base amid reports that at least one person had been injured.
The Ukrainian soldiers were later gathered at the base main square in front of the heavily armed Russian troops.
The storming followed an ultimatum by the Russians to surrender.
The Belbek base commander earlier told the few dozen troops still there to shoot in the air if they were attacked. He said he had been waiting for days for orders from Kiev but told the BBC that none had been issued.
Ukraine's military chiefs deny this, saying each unit in Crimea has been issued with clear orders on what to do if attacked.
In Novofedorivka, attackers threw smoke bombs at the base.
"All is in smoke. We retreated to the main headquarters," said Ukrainian defence ministry spokesman Vladyslav Seleznyov.
He later said Ukrainian forces had left the base after performing the national anthem.
Pro-Russian militia backed by Russian forces have already seized a number of Ukrainian bases in the southern peninsula.
"All of Crimea is Russia, and the Ukrainian force must leave," one of the pro-Russian activists told the BBC.
Russian troops have taken over control of Crimea following last month's overthrow of Ukrainian President Viktor Yanukovych.
The Kremlin said it acted to protect its "compatriots" in Crimea from "fascists" moving in from the mainland Ukraine.
Kiev denies the claim, accusing Moscow of "blatant lies" to justify the land grab.
Ukraine and the West have condemned as "illegal" the 16 March referendum in Crimea, where voters backed a proposal to re-join Russia.
The US and EU have responded with a series of sanctions targeting those individuals - including senior officials - involved in what Washington and Brussels describe as Crimea's "annexation".