Crimea’s regional parliament voted to join Russia on Thursday, a move that was immediately criticized by Western leaders, who have accused Russia of occupying the Ukrainian Black Sea peninsula.

The vice premier of the Crimea, which headquarters Russia’s Black Sea Fleet in Sevastopol, said a referendum on the region’s status would take place in ten days. If the majority ethnic Russian population votes in favor of joining the Russian Federation, which seems likely, all state properly will be nationalized, he said, and Ukrainian troops treated as occupiers and forced to leave.

Russian troops entered the Crimea in late February after Ukraine’s elected president, Viktor Yanukovich, was deposed following months of protests against his decision to pull out of an associated agreement with the European Union in favor of deeper ties with his country’s former Soviet master, Russia.

Russian president Vladimir Putin denied on Tuesday that his soldiers had seized the Crimea, arguing that he was acting on Yanukovich’s request for help and would use force as a “last resort” to protect Russian speakers and Russian interests in eastern Ukraine.

Western countries see Russia’s actions as naked aggression aimed at annexing a region that was part of the Russian Empire for almost two centuries before Soviet leader Nikita Khrushchev transferred it to Ukraine in 1954.

“The proposed referendum on the future of Crimea would violate the Ukrainian constitution and violate international law,” American president Barack Obama told reporters at the White House in Washington DC.

“Any discussion about the future of Ukraine must include the legitimate government of Ukraine,” he added.

Earlier in the day, Canada’s prime minister Stephen Harper said his country “will not recognize a referendum held in a region currently under illegal military occupation.”

The new government in Kiev has shied away from challenging Russia’s intervention in the Crimea but Prime Minister Arseniy Yatseniuk, a former economy and foreign minister, said the military would act if Russia pushed deeper into Ukrainian territory. “We are ready to protect our country,” he said.

In Brussels, European Council president Herman Van Rompuy offered Ukraine extensive aid and trade benefits after consultations with European leaders. The bloc warned Russia that unless it started negotiations with Ukraine and international partners, the European Union would impose travel bans for Russian officials and freeze their assets abroad.