Ukraine's parliament has called on the United States and Britain to uphold a pact signed with Russia to guarantee its sovereignty as tensions spiralled over the Crimea region.
Interim leader Oleksandr Turchynov also told MPs that he was summoning the country's security and defence chiefs over the crisis.
Legislators voted to demand guarantees of a 1994 memorandum that Ukraine signed with the Britain, Russia and the United States in Budapest safeguarding its borders and independence in return for giving up any nuclear arsenals left in the country after the collapse of the Soviet Union.
Ukraine's interior minister on Friday accused Russian forces of staging an "armed invasion" in Crimea, claiming they had blocked one air base and entered another airport overnight on the Black Sea peninsula.
The alleged raids - denied by Russian officials - came a day after pro-Russian gunmen seized control of Crimea's regional parliament and government building and local MPs voted to hold a referendum on May 25 to expand the region's autonomy from Kiev and replaced the local government with a pro-Moscow official.
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The growing tensions follow the removal of Kremlin-allied Ukraine president Viktor Yanukovych last weekend in an avalanche of change following the deaths of scores of people in clashes in Kiev.
