Russian troops took control of another Ukrainian naval base in Crimea late on Wednesday, a Ukrainian naval officer said.

Maj. Eduard Kusnarenko said there was no violence as Russian troops seized the naval transportation facility in Bakhchisaray, about 30 kilometres southwest of the regional capital Simferopol.

"Russian troops came and asked us to leave the base, which we did," he told Reuters news agency outside the base. "We will try again tomorrow to return to our post."

Russian troops reportedly fired a shot in the air as journalists tried to approach the gate to the base.

News of the second naval base seizure came shortly after Ukraine proposed that Crimea be declared a demilitarized zone by the UN with a pullout by both Russian and Ukrainian forces.

"The Ukrainian government will immediately appeal to the United Nations to recognize Crimea as a demilitarized zone and take necessary measures for Russian forces to leave Crimea and prepare conditions for re-deployment of Ukrainian forces," security chief Andriy Parubiy said.

Parubiy told journalists that in the face of the growing likelihood of military confrontation with Russia, the Ukrainian foreign ministry had been given the task of introducing visas for Russians visiting the ex-Soviet republic.

Referring to his demilitarization proposal, Parubiy, secretary of the National Security and Defence Council, said he hoped the United Nations would support the idea.

"This formula is the best for deescalation ... We hope that common sense will prevail," he said.

He also said Ukraine will hold military manoeuvres with the countries that signed the 1994 Budapest Memorandum. He didn't elaborate.

The document was signed by the U.S., Britain and Russia to guarantee Ukraine's territorial integrity when it surrendered its share of Soviet nuclear arsenals to Russia after the Soviet Union broke up in 1991. Ukraine has accused Russia of breaching the agreement by taking over the Crimean Peninsula.

In addition, Parubiy said Ukraine decided to leave the Moscow-dominated Commonwealth of Independent States, a loose alliance of 11 former Soviet nations. The last nation to leave the group was Georgia, which lost a brief war with neighbouring Russia in 2008 and ended up losing two separatist territories.

The announcement comes only hours after masked Russian-speaking troops seized control of Ukraine's naval headquarters in Crimea after it was stormed by militiamen. Pro-Moscow Crimean authorities also detained the Ukrainian navy commander and reportedly blocked the defence minister and another government official from travelling to the peninsula in what they said was a bid to defuse tensions.

Ukraine's military, which is heavily outnumbered in Crimea, has come under increased pressure since the region was nominally incorporated into Russia on Tuesday. 

Kiev threatens retaliation 

Central powers in Kiev have now threatened Crimean authorities with reprisals if "provocations" against Ukrainian troops on the peninsula continued, after Russian troops seized control of Ukraine's Crimean naval base and raised the Russian flag.

The tense but peaceful takeover of the the Ukrainian naval headquarters in the Black Sea port of Sevastopol signalled Moscow's intent to neutralize any armed opposition.

In Kyiv, acting President Oleksander Turchinov threatened to take action if pressure on Ukrainian forces in Crimea did not stop.

"If by 2100 [9 p.m.] all provocations against Ukrainian troops have not stopped and Admiral Haiduk and all other hostages ... are not released, the authorities will take appropriate measures, including of a technical and technological nature," he said in a statement posted online.

Most of Crimea's electricity, water and food is supplied from the Ukrainian mainland and Turchinov's comments suggest Kyiv could be prepared to squeeze the supplies.

Ukrainian commander captured

The several hundred militiamen who captured the base in Sevastopol met no resistance. Sevastopol is also the home port of Russia's Black Sea Fleet, and tens of thousands of Russian-led troops are now patrolling Crimea.

It came a day after a confrontation between Ukrainian soldiers and pro-Russian militia left two dead.

The Russian-speaking troops, who arrived on the base after the storming, wore helmets, flak jackets and uniforms with no identifying insignia. By afternoon, they were in full control of the naval headquarters, a set of three-story boxy white concrete buildings with blue trim. It was not immediately clear how many, if any, Ukrainian servicemen remained on the base.

Ukraine's Defence Ministry said no one was injured in the raid, which it said was led by pro-Russian militiamen and Cossacks.

The ministry said in its statement that Rear Adm. Sergei Haiduk was detained by unknown people after the storming of the fleet headquarters. The Russian state ITAR-Tass news agency reported that he was being questioned by Crimean prosecutors.

Ukraine's defence minister and deputy prime minister had planned to travel to Crimea on Wednesday in what they said was a bid to avert an escalation in hostilities.

Russia vs. Ukraine military infographic

(Duk Han Lee/CBC)

The prime minister in Crimea warned after the announcement of their departure that they would be turned back, however.

"They are not welcome in Crimea," Sergei Aksyonov was quoted as saying by the Interfax news agency. "They will not be allowed to enter Crimea. They will be sent back."

Interfax later cited Welfare Minister Lyudmila Denisova as saying the officials had been denied entry to Crimea. She said an emergency session of the National Security and Defence Council will held in response.

At the Ukrainian navy headquarters, an Associated Press photographer said the militiamen took down the gate and made their way onto the base. They then raised the Russian flag on the square by the headquarters.

The unarmed militiamen waited for an hour on the square and, following the arrival of the commander of the Russian Black Sea Fleet, they took over the building.

The AP photographer was able to enter the headquarters and saw the militia roaming around while the Ukrainian servicemen were packing up and leaving.

U.S. will respond to any threat to NATO allies: Biden

Issuing an outright warning to Moscow, Vice President Joe Biden declared Wednesday the United States will respond to any aggression against its NATO allies, as Russia's neighbours looked warily to the escalating crisis in nearby Ukraine.

Standing side by side with a pair of Baltic leaders in Vilnius, Lithuania, Biden said the U.S. was "absolutely committed" to defending its allies, adding that President Barack Obama plans to seek concrete commitments from NATO members to ensure the alliance can safeguard its collective security.

In a jab at Russia, he said the U.S. stands resolutely with Baltic states in support of the Ukrainian people against Russian aggression.

"Russia cannot escape the fact that the world is changing and rejecting outright their behaviour," Biden said, after meeting in Vilnius with Lithuanian President Dalia Grybauskaite and Latvian President Andris Berzins.

Biden's comments came at the close of a two-day trip to Lithuania and Poland with a two-pronged theme: Sending a stern message to Russian President Vladimir Putin that the U.S. won't abide Russian intervention in Ukraine, and reassuring fretful NATO allies that the U.S. and others will come to their defence if necessary.

Biden also told reporters on Tuesday that the U.S. may run more ground and naval military exercises to help Baltic states near Russia beef up their capacity after what he called Russian President Vladimir Putin's "land grab" in Ukraine.

Any additional military exercises in the Baltics would build on measures already taken, officials said. The Pentagon increased the number of U.S. aircraft in regular NATO air patrols over the Baltics, and it beefed up a previously planned training exercise with the Polish air force.

Meanwhile on Wednesday, the head of NATO warned that Putin may not stop with the annexation of Crimea and urged Europe to step up defense spending in response to the crisis.

"Crimea is one example. But I see Crimea as an element in a greater pattern, in a more long-term Russian, or at least Putin, strategy," Secretary-General Anders Fogh Rasmussen told a Washington think tank. "So of course our major concern now is whether he will go beyond Crimea."

U.N. chief Ban Ki-moon meets Putin in Moscow on Thursday and travels to Kiev on Friday. He will urge a peaceful end to a crisis that began when Ukraine's president abandoned a trade pact with the European Union and turned instead to Moscow, prompting violent street protests that led to his overthrow.

Russia moves forward with Crimea annexation plans

Russian news agencies on Wednesday quoted Valery Zorkin, chairman of the Russian Constitutional Courts, telling reporters that they have just ruled the treaty to be valid, thus clearing yet another hurdle for Russia to annex Crimea.

The treaty will now only need to be ratified by the Russian parliament.

Russian Finance Minister Anton Siluanov said Russia will cover Crimea's budget deficit — estimated at 55 billion rubles, about $1.7 billion Cdn.

Siluanov, speaking on state television, said the money would come from Russia’s federal budget.

Additionally, a senior Russian diplomat says Moscow may change its stance in the Iranian nuclear talks in light of the rising tensions with the West.

Deputy Foreign Minister Sergei Ryabkov was quoted Wednesday afternoon as saying by the Interfax news agency that Russia didn't want to use the Iranian nuclear talks to "raise stakes," but may have to do so in response to the actions by the United States and the European Union.

The statement is the most serious threat of retaliation by Moscow after the U.S. and the EU announced sanctions against Russia over the Ukrainian crisis.    

Similarly, at a meeting of the Organization for Security and Cooperation in Europe in Vienna on Wednesday afternoon, Russia was the sole objector to vote against a resolution to send observers to Crimea. 

The West and Ukraine described the Crimean referendum as illegitimate and being held at gunpoint.

The United States and the European Union on Monday imposed sanctions on Russia, targeting Russian and Crimean officials with visa bans and asset freezes.

With files from The Associated Press