The protesters had seized the first floor but were unable to go higher because lifts were disabled and stairwell doors shut, Reuters reported.

The 11-storey building has been flying the Russian flag, rather than the Ukrainian flag, for three days, with demonstrators carrying Russian flags staging rallies outside.

This is while Ukraine accused Russia on Monday of pouring extra troops and military planes into Crimea.

Russian Foreign Minister Sergei Lavrov said the troops were needed in the flashpoint Black Sea peninsula until "the stabilization of the situation" in Ukraine, and criticized the West for its threats of "sanctions and boycotts".

Crimea -- a strategic Black Sea peninsula with a majority ethnic Russian population -- has been under control of pro-Kremlin troops since President Vladimir Putin won parliament's authorization Saturday to use security troops in Ukraine.

The price of oil surged on fears of an all-out conflict as the Kremlin looked set to send troops into eastern Ukraine -- a vast industrial region with close ties to Russia that Putin has vowed to protect from "ultranationalist forces".

Ukraine has soared to the top of the global agenda even as the conflict in Syria rages drastically.

The crisis on the eastern edge of Europe threatens to blow up into the biggest test to global diplomacy since the fall of the Berlin Wall.

 NJF/NJF