The Ukrainian government launched an "anti-terror" operation Tuesday against pro-Russia activists in the eastern city of Donetsk following a new wave of unrest over the weekend.

During a similar operation in Slavyansk in Donetsk region, Ukrainian security forces exchanged gunfire with pro-Russia protesters, causing casualties on both sides.

In what appeared to be the most forceful response to the pro-Russia protests in nearly 10 cities, Kiev deployed 20 tanks and armored personnel carriers to the eastern region, according to media reports.

Pro-Russia activists, demanding a referendum on autonomy and closer ties with Russia, seized several government buildings in the cities of Donetsk, Lugansk and Kharkov over the weekend.

The unrest in Ukraine's Russian-speaking east came after Russia absorbed the Ukrainian peninsula of Crimea on March 18 after a referendum.

The United States urged Kiev to act "gradually" and "responsibly" in handling the tensions.

"We urge the Ukrainian government to move forward gradually, responsibly, and with all due caution as it deals with the situation caused by armed militants who have seized government buildings, established roadblocks illegally in parts of the country," White House spokesman Jay Carney told reporters on Tuesday.

He stressed that Washington was continuing its efforts to seek a diplomatic solution, saying: "As the president has said, we do not see a military solution to this crisis."

For its part, Russia has warned Ukraine against using force to restore order in the country's east, saying that step would end future cooperation.

Moscow said Tuesday that it has halted the transfer of military equipment and weaponry in Crimea to Ukraine. It also warned the West against weapons deliveries to Ukraine.

Russia and West face the worst standoff since the end of the Cold War after Russia absorbed Crimea. Washington and Brussels imposed a wave of sanctions against Moscow.

However, EU, Russian, Ukrainian and US diplomats are planning to meet for direct talks on the Ukraine crisis in Geneva Thursday, the first of its kind during the months-old crisis.

Ukraine's ambassador to the United Nations Office at Geneva said on Tuesday that the upcoming four-party talks aim to seek ways to de-escalate the situation on its border rather than focus on its internal affairs.

Yurii Klymenko told a press conference that the meeting would be about finding ways to de-escalate the situation on the ground and restore trade and economic relations between Moscow and Kiev.

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