People gathered in front of the Crimean parliament in Simferopol on Saturday as armed men patrolled the area nearby.
Sergei Aksyonov, the prime minister of Crimea, has called on Vladimir Putin, for help, saying he was “recognising” his “responsibility for the lives and security of the people.”
“I ask Russia’s President Vladimir Putin to offer assistance in providing peace and order in the Autonomous Republic of Crimea.”
Putin has responded by asking the upper house of Russia’s parliament to approve the use of Russian armed forces in Ukraine, according to a statement from the Kremlin.
The Russian foreign ministry says it is “extremely concerned” about the situation in the region.
But Ukraine’s prime minister, Arseniy Yatsenyuk, has appealed to Russia to halt military movements in the autonomous republic.
On Saturday, Ukraine’s defence minister said Russia had “recently” brought 6,000 additional personnel into Ukraine.
Meanwhile, the Russian Foreign Ministry announced Russia’s Consulate General in Crimea will give out Russian passports to servicemen in Ukraine’s controversial and now-disbanded Berkut riot police.
Protesters in Ukraine had accused the force of firing live bullets at demonstrators, killing dozens of people.