The White House on Friday urged Russia to respect the territorial integrity of Ukraine, while Russia's president stressed to European leaders the need to "normalize" the situation there.
White House spokesman Jay Carney said reports of Russian intervention in the southern Ukrainian region of Crimea are of "deep concern" to the United States, and he reiterated comments made by other U.S. officials that intervention in Ukraine would be a "grave mistake."
Carney said Washington is seeking clarification of reports of Russian intervention in Crimea, where pro-Russian gunmen seized government buildings Thursday.
On Friday, Ukraine's interim interior minister Arsen Avakov said Russian forces took control of Crimea's two main airports. He said armed Russian troops were blocking the Belbek airport in Sevastopol, where Russia has a naval base.
A VOA correspondent who flew into Crimea's Simferopol Airport on Friday saw gunmen wearing camouflage and carrying automatic weapons at the airport.
Meanwhile, the Kremlin said in a statement Friday that President Vladimir Putin discussed the situation in Ukraine in telephone conversations with British Prime Minister David Cameron, German Chancellor Angela Merkel and European Council Chairman Herman Van Rompuy.
According to the Kremlin, the conversations emphasized the need to prevent a further escalation of violence and quickly normalize the situation in Ukraine.
On Thursday, the Kremlin reported that Mr. Putin had instructed his government "to continue contacts with partners in Kyiv on the issues of development of trade and economic ties between Russia and Ukraine."