An officer has been killed in an attack on a base in Crimea, the Ukrainian military has revealed.
The death in the region's main town Simferopol is the first such death since pro-Russia forces took control last month and Ukraine has now given its troops the authority to use force to defend themselves.
Ukraine's prime minister, Arseny Yatseniuk, has denounced the assault on the base by unknown attackers as a "war crime" and called for international talks to prevent an escalation of the conflict.
"Today, Russian soldiers began shooting at Ukrainian servicemen and this is a war crime without any statute of limitations," he told a meeting at the defence ministry.
Acting President Oleksander Turchinov, referring to Nazi Germany, told the meeting: "Putin today is copying the fascists from the last century by annexing the territory of another independent country recognised by the entire world."
A defence ministry statement said the dead man had been shot while manning a tower, adding that the attackers in Russian uniforms were holding the base commander in a nearby building, Reuters reported.
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A junior officer who was on duty in a park inside the base was killed and another officer injured, according to the Ukraine government. A third serviceman suffered leg and head injuries after being beaten, the BBC said..
The attack came soon after Vladimir Putin had launched a blistering offensive on the West's "baffling, primitive, and blatant" posturing over Crimea, quipping that it is "better late than never" for the West to take the lead on observing international law.
In a speech to the Duma, the Russian president accused the West of fermenting a "precedent with their own hands." Russian and Crimean leaders have now signed a treaty to make the territory part of Russia.
His words were trenchant. "In a situation absolutely the same as the one in Crimea they recognised Kosovo’s secession from Serbia as legitimate, while arguing that no permission from a country’s central authority for a unilateral declaration of independence is necessary," Putin said.
President Putin drew condemnation after he announced new laws allowing Crimea to join the Russian Federation.
David Cameron accused Moscow of a "flagrant breach of international law" in trying to annex the region on the basis "of a sham referendum held at the barrel of a Russian gun".
"President Putin should be in no doubt that Russia will face more serious consequences and I will push European leaders to agree further EU measures when we meet on Thursday," the prime minister said.
Meanwhile, the former Soviet president Mikhail Gorbachev has entered the debate over Crimea, saying the referendum among the peninsula's voters has corrected an historical "mistake".
"While Crimea had previously been joined to Ukraine based on the Soviet laws, which means [Communist] party laws, without asking the people, now the people themselves have decided to correct that mistake," the Moscow Times reported the ex-premier as saying.
"This should be celebrated, not sanctioned," he said.