Ukraine will respond with military action if Russia attempts to annex the country's mainly Russian-speaking eastern regions, interim prime minister Arseniy Yatsenyuk said on Thursday.
"I want to officially warn Russia: we will respond firmly, including through military means, against any attempt to seize Ukraine, to cross borders, or annex eastern or other regions by Russian troops," Yatsenyuk was quoted as saying in Brussels on the government website.
Yatsenyuk also appealed to the West to "respond appropriately" as Moscow moves to attach Ukraine's Crimea Peninsula to the Russian Federation.
"Russia has violated international law and undermined the nuclear non-proliferation regime," the premier said.
"Russia has carried out an armed robbery against an independent neighbouring country."
Under a milestone agreement in 1994, Russia agreed to respect Ukraine's territorial integrity while Kiev renounced its Soviet-era nuclear arms.
"Everyone should understand that there is a price to pay for stability in the world," said Yatsenyuk.
"There are two means: either with victims (of a conflict) or with euros and dollars," he said in reference to economic sanctions.
"It is better to sacrifice euros and dollars than to cry over thousands of deaths in a bloody war.
"I hope that our European partners understand that. Afterwards it will be too late to use other types of sanctions," he added.