Armed men thought to be Russians drove a truck into a Ukrainian missile-defence post in the Crimea region on Friday but a standoff was resolved without a shot being fired, witness said.

Initial reports said the truck had smashed through the gates of the base in the port city of Sevastopol and that it was being stormed, but a Reuters reporter on the scene could not see any signs of major damage to the gates and the base was quiet.

Crimea's pro-Russia premier, Sergei Aksyonov, was asked about the incident during a political chat show shown live on Ukrainian television and said all was calm at the military post.

Referring to the armed men as "self-defence units, he indicated the standoff was over, adding: "Now the self-defence units are surrounded by journalists. There are no attempts to attack."

A Ukrainian military official told Reuters at the post that the armed group inside had not seized any weapons.

The news comes on the same day Russian President Vladimir Putin's spokesman lashed out at the West and defended the country's actions in Ukraine, but said he hoped a new Cold War would not break out despite "extremely deep disagreements."

In a telephone conversation with U.S. Secretary of State John Kerry, Foreign Minister Sergei Lavrov warned against "hasty and reckless steps" that could harm Russian-American relations, the foreign ministry said.

"Sanctions ... would inevitably hit the United States like a boomerang," it added.

Crimea sets referendum date

It was the second tense, high-level exchange between the former Cold War foes in 24 hours.

Russian President Vladimir Putin said after an hour-long call with U.S. President Barack Obama that they were still far apart on the situation in the former Soviet republic. Obama announced the first sanctions against Russia on Thursday.

Ukraine's border guards said Moscow had poured troops into the southern peninsula where Russian forces have seized control.

Serhiy Astakhov, an aide to the border guards' commander, said there were now 30,000 Russian soldiers in Crimea, compared to 11,000 permanently based with the Russian Black Sea fleet in the port of Sevastopol before the crisis.

Putin denies that the forces with no national insignia that are surrounding Ukrainian troops in their bases are under Moscow's command, although their vehicles have Russian military plates. The West has ridiculed this claim.

Crimea's parliament, dominated by ethnic Russians, set a referendum for joining Russia for March 16. European Union leaders and Obama denounced the referendum as illegitimate, saying it would violate Ukraine's constitution.

The head of Russia's upper house of parliament said after meeting visiting Crimean lawmakers on Friday that Crimea had a right to self-determination, and ruled out any risk of war between "the two brotherly nations."

Guerrilla war?

Senior Ukrainian opposition politician Yulia Tymoshenko, freed from prison after former president Victor Yanukovich's ouster, has appealed for immediate EU sanctions against Russia, warning that Crimea might otherwise slide into a guerrilla war.

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A uniformed man, believed to be a Russian serviceman, stands guard near a Ukrainian military base outside the city of Sevastopol. (David Mdzinarishvili/Reuters)

Brussels and Washington rushed to strengthen the new authorities in economically shattered Ukraine, announcing both political and financial assistance.

The regional director of the International Monetary Fund said talks with Kyiv on a loan agreement were going well and praised the new government's openness to economic reform and transparency.

The European Commission has said Ukraine could receive up to $15 billion US in the next couple of years provided it reaches agreement with the IMF, which requires painful economic reforms like ending gas subsidies.

Promises of billions of dollars in Western aid for the Kyiv government, and the perception that Russian troops are not likely to go beyond Crimea into other parts of Ukraine, have helped reverse a rout in the local hryvnia currency.

New government wants troops out

Ukrainian Prime Minister Arseny Yatseniuk said no one in the civilized world would recognize the result of the "so-called 
referendum" in Crimea.

He repeated Kyiv's willingness to negotiate with Russia if Moscow pulls its additional troops out of Crimea and said he had requested a telephone call with Russian Prime Minister Dmitry Medvedev.

But German Foreign Minister Frank-Walter Steinmeier said  there was no clear signal that Russia was willing to join an 
international "contact group" with Ukraine proposed by the West  to negotiate a solution to the crisis.

Ukrainians confident

Demonstrators who have remained encamped in Kyiv's central Independence Square to defend the revolution that ousted Yanukovych have mixed reactions to any potential secession.

They are "certainly concerned about the referendum in Crimea — what that means for family there, for holidays there," CBC's Susan Ormiston said from Ukraine.

"They see it as a foregone conclusion that Crimea will take that vote and decide to join Russia.”

Despite Putin's tough words, however, many demonstrators who have remained in Kyiv's central Independence Square said they did not believe Crimea would be allowed to secede.

Some said they were willing to go to war with Russia, despite the mismatch between the two countries' armed forces.

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Russian President Vladimir Putin and U.S. President Barack Obama spoke on the phone for an hour Thursday. (Reuters)

Unarmed military observers from the pan-European Organisation for Security and Cooperation in Europe were blocked from entering Crimea for a second day in a row on Friday, the OSCE said on Twitter.

CBC correspondent Nahlah Ayed tweeted from Crimea: "After three negotiation attempts, military observers likely to stop trying to get to Crimea [Friday night], will try again tomorrow." 

The observers would be able to make the first independent look at whether the troops are Russian or are "local self-defence forces," as Putin has claimed.

The streets largely belong to people who support Moscow's rule, some of whom have become increasingly aggressive in the past week, harassing journalists and occasional pro-Kyiv protesters.

Part of the Crimea's two million population opposes Moscow's rule, including members of the region's ethnic Russian majority. 

Ayed said Crimeans who oppose joining Russia held a gathering in Simferopol on Friday that they took pains to say was not a protest, but a rally for peace.

"They want to be able to disagree with the idea of this place joining Russia without leading to violence," she said.

With files from CBC News, The Associated Press