Sevastopol - Pro-Russian forces captured Ukraine's naval commander after seizing his headquarters in Crimea on Wednesday as Moscow's grip tightened on the peninsula despite Western warnings its “annexation” would not go unpunished.
Kiev said it was dispatching its defence minister but Crimea's regional leader said he would be barred from entry amid mounting tensions in a region at the epicentre of the worst East-West standoff since the Cold War.
Dozens of despondent Ukrainian soldiers - one of them in tears - filed out of the Ukraine's main navy base in the Black Sea port city of Sevastopol after its storming by hundreds of pro-Kremlin protesters and Russian troops.
“We have been temporarily disbanded,” a Ukrainian lieutenant who identified himself only as Vlad told AFP.
“I was born here and I grew up here and I have been serving for 20 years,” he said as a Russian flag went up over the base without a single shot being fired in its defence. “Where am I going to go?”
A Russian forces' representative said that Ukraine's navy commander Sergiy Gayduk - appointed after his predecessor switched allegiance in favour of Crimea's pro-Kremlin authorities at the start of the month - had been detained.
“He was blocked and he had nowhere to go. He was forced out and he has been taken away,” Igor Yeskin told reporters.
A defence ministry spokesman in Crimea said pro-Russian forces also seized the checkpoint set up in front of a Ukrainian military base in the region's western port town of Novoozerne.
He said they used a tractor to ram open the gate and were now in a standoff with Ukrainian troops.
The Ukrainian government dispatched acting Defence Minister Igor Tenyukh and First Deputy Prime Minister Vitaliy Yarema to the region for urgent mediation talks.
But Crimea's self-declared prime minister Sergei Aksyonov told the Interfax news agency while on a visit to Moscow that “no one will let them into Crimea and they will be sent back.”
A defiant President Vladimir Putin had brushed aside global indignation and Western sanctions on Tuesday to sign a treaty absorbing Crimea and expanding Russia's borders for the first time since World War II.
Russia's Constitutional Court ruled unanimously on Wednesday that the “treaty complies with the Russian Constitution.”
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 Crimea - a heavily Russified region the size of Belgium that is home to two million people.
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.
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.
“We are not speaking about military actions in the eastern regions of Ukraine,” Putin's spokesman Dmitry Peskov told the BBC.
“But Russia will do whatever is possible... to protect and to extend a hand of help to Russians living in eastern regions of Ukraine.”
Putin had signed the Crimea treaty - 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 on Tuesday.
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”.
The Ukrainian defence ministry soon authorised its soldiers 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 fully-fledged Russian offensive.
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 sides to “take all possible steps to avoid further escalation.”
And German Chancellor Angela Merkel Ä seen as the most important potential powerbroker in the crisis Ä 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.
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.