Ukraine's interim president says he has launched a crackdown on pro-Russian demonstrators who have taken over state buildings in eastern Ukraine.
Oleksander Turchynov told lawmakers Tuesday that government forces have begun an operation in the region of Donetsk, where pro-Moscow forces have ignored Kyiv's previous ultimatum to surrender by Monday or face retaliation.
Mr. Turchynov told lawmakers the crackdown was being carried out gradually and cautiously.
Pro-Russian demonstrators fortified their positions late Monday and erected fresh barricades, despite the government warning.
Western governments have accused Moscow of backing the protests in eastern Ukraine. U.S. President Barack Obama warned Russian President Vladimir Putin in a phone call Monday that Moscow will face further costs if its actions in Ukraine persist. He also urged the Russian leader to use his influence to persuade the demonstrators to leave the buildings they have seized.
In turn, Mr. Putin urged Mr. Obama to discourage the Ukrainian government from using force against protesters.
He denied claims of Russian agents' involvement in the protests as "speculations based on unreliable information.'' Mr. Putin said the protests vented public anger about the Ukrainian government's reluctance to recognize the interests of Russian speakers in the east.
The demonstrators are demanding a referendum on whether to split with Ukraine and join Russia - similar to last month's vote in Crimea.
Mr. Turchynov said he is not against a national referendum on what kind of country Ukraine should be. He said he is certain a majority would support a united and independent Ukraine, possibly giving broader localized rights to the east. He said such a vote could be held at the same time as the May 25 presidential election.
In Moscow, Russian Foreign Minister Sergei Lavrov said Monday he believes Russian-speaking Ukrainians in the eastern part of the country should be part of drafting a new constitution.
Top diplomats from Russia, the United States, Ukraine and the European Union are to hold emergency talks on the crisis April 17 in Geneva. White House officials say U.S. Vice President Joe Biden will travel to Kyiv April 22.
Meanwhile, U.S. officials signed a $1 billion loan guarantee to Ukraine. U.S. Treasury Secretary Jacob Lew said the agreement demonstrates the United States' unwavering commitment to a stable Ukraine. Ukrainian Finance Minister Oleksandr Shlapak said his country is wrapping up talks with the IMF on a comprehensive economic reform program.