MOSCOW - Tensions in Crimea were heightened late in the evening Friday when pro-Russian forces tried to seize a Ukrainian military base in the port city of Sevastopol, Interfax news agency reported.
No shots were fired, but stun grenades were thrown, according to the report, citing Ukrainian officials.
About 100 Ukrainian troops are stationed at the base and they barricaded themselves inside one of their barracks, and their commander began negotiations, Interfax said. Crimea's pro-Moscow leader denied any incident at the base.
Meanwhile, unarmed military observers from the pan-European Organization for Security and Cooperation in Europe were blocked from entering Crimea on Friday for a second day, the OSCE said on Twitter.
CBS News correspondent Elizabeth Palmer reported from the Crimean capital, Simferopol, that when international monitors first showed up at the border between Ukraine and Crimea, armed men would not let them in.
Security camera footage show a European photographer - attacked and threatened with a gun to his head after he took pictures of other journalists being beaten and robbed, Palmer reports.
In Russia, which was swept up in patriotic fervor for bringing Crimea back into its territory, tens of thousands of people thronging Red Square waving flags and chanting "Crimea is Russia!" as a parliamentary leader declared that the peninsula would be welcomed as an "equal subject" of Russia.
The semi-autonomous region belongs to Ukraine, but the local parliament has called a March 16 referendum on whether Crimea should join Russia, a move President Barack Obama has called a violation of international law.
In the week since Russia seized control of Crimea, Russian troops have been neutralizing and disarming Ukrainian military bases on the Black Sea peninsula. Some Ukrainian units, however, have refused to surrender.
Crimea's new leader has said pro-Russian forces numbering more than 11,000 now control all access to region and have blockaded all military bases that have not yet surrendered.
Foreign Minister Sergey Lavrov warned U.S. Secretary of State John Kerry that sanctions over Russian actions in Crimea could backfire, the ministry said in a statement. In a telephone conversation, Lavrov urged the U.S. not to take "hasty, poorly thought-out steps that could harm Russian-U.S. relations, especially concerning sanctions, which would unavoidably boomerang on the U.S. itself," the statement said.
The strategic peninsula has become the flashpoint in the battle for Ukraine, where three months of protests sent President Viktor Yanukovych fleeing to Russia. Moscow calls the new Ukrainian government illegitimate, and has seized control of Crimea, where it has a major naval base on the Black Sea.
Although President Vladimir Putin said Tuesday that Russia has no intention of annexing Crimea, he insisted that its residents have the right to determine the region's status in the referendum.
Valentina Matvienko, the speaker of Russia's upper house of parliament, made clear Friday the country would welcome Crimea if it votes in the referendum to join its giant neighbor. About 60 percent of Crimea's population identifies itself as Russian.
"If the decision is made, then (Crimea) will become an absolutely equal subject of the Russian Federation," Matvienko said during a visit from the chairman of the Crimean parliament, Vladimir Konstantinov. She spoke of mistreatment of Russian-speaking residents in Ukraine's east and south, which has been Moscow's primary argument for possible intervention in Ukraine.
The Russian parliament is scrambling to make it easier for Crimea to join Russia. Russia's constitution allows the country to annex territory only by an agreement "initiated... by the given foreign government." That would entail signing an agreement with the new authorities in Kiev, whom Moscow does not recognize.
On the other side of Red Square from the parliament building, 65,000 people gathered at a Kremlin-organized rally in support of Crimea.
"We always knew that Russia would not abandon us," Konstantinov shouted from the stage. He also called on Moscow not to forget other Russia-leaning regions in Ukraine.
"We must not leave the Ukrainian people at the mercy of those Nazi bandits," he said, referring to the new government in Kiev.
Russian state gas company Gazprom also increased the pressure on Ukraine's new government, which now owes $1.89 billion for Russian natural gas. Gazprom chief executive Alexei Miller said if Ukraine doesn't pay off its debt, "there is a risk of returning to the situation of the beginning of 2009" when Russia cut off supplies to Europe because of a pricing dispute with Ukraine.
The new government, which is struggling to stabilize Ukraine's finances and failing economy, got encouraging news Friday from the International Monetary Fund, which said that economic assistance was on the way.
"I am positively impressed with the authorities' determination, sense of responsibility and commitment to an agenda of economic reform and transparency, Reza Moghadam, the IMF's European Department director, said in a statement after a two-day visit. "The IMF stands ready to help the people of Ukraine."
Russia has denied that its forces are active in Crimea, describing the troops who wear green uniforms without insignia as local "self-defense forces." But many of the troops, who are armed with advanced heavy weaponry, are being transported by vehicles with Russian license plates.
Hoping to pressure Russia to roll back its military presence, the United States imposed financial sanctions and travel bans on Russians and other opponents of the new Kiev government on Thursday. The European Union suspended talks with Russia on a wide-ranging economic agreement and on granting Russian citizens visa-free travel to the 28-nation bloc, a long-standing Russian objective.
Putin opened the Winter Paralympics in Sochi on Friday against the backdrop of his country's military action in Crimea. A solitary Ukrainian athlete took part in the opening ceremony.
Ukraine delivered a pointed message by sending out only a single flag-bearer to represent the 23-strong team in the athletes' parade. The appearance of biathlete Mykhaylo Tkachenko drew a roar from the capacity crowd at the Fisht Olympic Stadium. Entering in a wheelchair with the Ukrainian flag, he wore a serious expression.
The Ukrainian team had announced only a few hours earlier that it would not boycott the games, but said it could pull out of the 10-day event if the Crimea situation escalates.
Crimea would be the first territory to join Russia since the breakup of the Soviet Union in 1991. South Ossetia and Abkhazia, which broke away from Georgia after a brief 2008 war with Russia, have been recognized as independent by Moscow, but there have been few serious moves to enable them to join Russia.
For Putin, Crimea would be a dazzling acquisition, and would help cement his authority with a Russian citizenry that has in recent years shown signs of restiveness and still resents the loss of the sprawling empire Moscow ruled in Soviet times.
In the Crimean capital, Simferopol, 75 people turned out Friday for a rally at the local monument to 19th-century Ukrainian poet Taras Shevchenko. They spoke both Ukrainian and Russian, but waved Ukrainian flags and released white doves into the rainy sky.
One of those at the protest was native Russian speaker Anton Romanov, who said he opposes the occupation of Crimea by Russian troops.
"I'm against being forced to live in a different country," he said.