SEVASTOPOL, Ukraine - Pro-Russian protesters stormed Ukraine's naval headquarters in Crimea on Wednesday after Moscow claimed the peninsula and the first casualties ratcheted up the stakes in the worst East-West crisis since the Cold War.
A Ukrainian navy spokesman said the crowd of a few hundred irate activists in Ukraine's port city of Sevastopol had forced a group of officers to barricade themselves inside the building to avoid a direct confrontation.
"There are about 200 of them, some wearing balaclavas. They are unarmed and no shots have been fired from our side," spokesman Sergiy Bogdanov told AFP.
"The officers have barricaded themselves inside the building," he said, adding that the officers had no intention of using their weapons.
A defiant President Vladimir Putin had brushed aside global indignation and Western sanctions on Tuesday to sign a treaty absorbing the flashpoint Ukrainian peninsula and expanding Russia's borders for the first time since World War II.
The historic and hugely controversial moment came less than a month after the ouster in Kiev of a Moscow-backed regime by leaders who spearheaded three months of deadly protests aimed at pulling Ukraine out of the Kremlin's orbit for the first time.
Putin responded by winning the right to use force against his ex-Soviet neighbour and then using the help of local militias to seize the Black Sea region of Crimea - the warm water outlet for Russian navies since the 18th century.
The explosive security crisis on the EU's eastern frontier now threatens to reopen a diplomatic and ideological chasm between Russia and Western powers not seen since the tension-fraught decades preceding the 1989 fall of the Berlin Wall.
"Russia's political and economic isolation will only increase if it continues down this path and it will in fact see additional sanctions by the United States and the EU," US Vice President Joe Biden warned on Tuesday while paying a visit to Poland aimed at reassuring former Soviet satellites of Washington's backing in the face of the Kremlin's expansionist threat.
The greatest fear facing Kiev's new leaders and the West is that Putin will push huge forces massed along the Ukrainian border into the Russian-speaking southeastern swathes of the country in a self-professed effort to "protect" compatriots who he claims are coming under increasing attack from violent ultranationalists.
Putin's spokesman Dmitry Peskov dismissed the speculation while still hinting strongly that Russia intended to play a big future role in Ukraine's domestic affairs.
"We are not speaking about military actions in the eastern regions of Ukraine," Peskov told the BBC.
"But Russia will do whatever is possible, using all legal means, all legal means, in total correspondence with international law, to protect and to extend a hand of help to Russians living in eastern regions of Ukraine."
Putin had signed the Crimea treaty - at this stage recognised by no nation besides Russia - after stressing the move was done "without firing a single shot and with no loss of life." But the first bloodshed came to the rugged peninsula of two million people only hours later when a group of gunmen wearing masks but no military insignia stormed a Ukrainian military centre in Simferopol.
The Ukrainian defence ministry said one of its soldier died from a neck wound and another suffered various injuries.
The pro-Russia Crimean police said a member of the local militias had also been killed. A spokeswoman blamed both casualties on shooting by unidentified assailants from a nearby location.
But the violence prompted Ukraine's Prime Minister Arseniy Yatsenyuk to warn an emergency government meeting that "the conflict is shifting from a political to a military stage.
"Russian soldiers have started shooting at Ukrainian military servicemen, and that is a war crime," the Wester-backed prime minister said.
The Ukrainian defence ministry soon authorised its soldier in Crimea to open fire in self defence for the first time.
Ukraine had previously forbidden its troops from shooting - in some cases forcing them to stand guard at their bases with empty rifles - to avoid provoking a offensive by its nuclear-armed giant that could spill into an all-out war.
NATO 'deeply concerned'
Reports of the crisis turning deadly and fears what Biden called a further "land grab" by Putin prompted both expressions of concern and recollections of the horrors of prior European conflicts.
NATO Secretary General Anders Fogh Rasmussen said he was "deeply concerned" and urged all side to "take all possible steps to avoid further escalation." US Secretary of State John Kerry likened the "nationalistic fervour" fuelled in Russia by the crisis to the build-up before World War II.
"All you have to do is go back and read in history of the lead-up to World War II and the passions that were released with that kind of nationalistic fervour," the top US diplomat said.
German Chancellor Angela Merkel - seen as the most important potential powerbroker in the crisis - said Russia was guilty of repeatedly breaking international law.
Moscow already risks expulsion from the G8 group of top nations and the promise of new US sanctions on top of Russian travel bans and asset freezes unveiled by the European Union and Washington on Monday.
US President Barack Obama called for a G7 summit next week in The Hague to discuss the escalating showdown.
Diplomats in Brussels said EU and Ukrainian leaders would on Friday sign the political portion of a landmark pact whose rejection by Yanukovych in November sparked the protests that led to his fall.