Security forces in eastern Ukraine launched an operation Sunday to eliminate pro-Russian separatists from a police headquarters in Slaviansk. Kiev is reporting deaths of both Ukrainians and Russians.

Rebellions in east Ukraine, which the country calls an act of agression by the Russians, could set off more violence, as Russia says it will protect their people if they come under under attack.

A Ukranian state security officer was killed and five on the government side were wounded. Interior minister Arsen Avakov called Sunday's operation an anti-terrorist operation.

Ukraine is accusing Russia of trying to intensify and continue the violence and chaos in Ukraine. Ukraine was a former Soviet republic that Russia once ruled.

Ukraine wants to get the country back to normalcy after months of turmoil. They believe the May 25 presdential elections will help, but accuse Russia of trying to undermine the election process.

Russia has already sent troops into Crimea in southern Ukraine saying that Russians there were under threat. Many in Western governments think they'll use this same reasoning to send troops to the eastern portion of Ukraine.

Avakov has already warned citizens to stay indoors. "Pass this on to all civilians: they should leave the centre of town, not come out of their apartments, and not go near the windows," he wrote on his Facebook page.

In nearby Kramatorsk, police and militants exchanged gunfire late Saturday. No deaths or injuries have been confirmed.

The White House is concerned that recent seizures of public buildings in eastern Ukraine could be a sign of a Russian sudden military attack. Russia has denied this.

The White House is warning Russian President Vladimir Putin and Russia to stop their efforts at destablizing Ukraine. Vice President Joe Biden will visit Kiev on April 22. He is the most senior official from the U.S. to visit Ukraine since the crisis began.

Russian Foreign Minister Sergei Lavrov warns of force against the Russians. He says the potential for cooperation between Russia and Ukraine would disappear if the Russians are faced with force.

NATO says Russia is beefing up its armed forces at the eastern border of Ukraine. Russia disagrees and says they are normal manuevers.

With the increase in efforts by pro-Russian groups, Ukranian commentator Sergei Leshchenko says Russia is trying to secure a strong negotiating position in advance to the upcoming international talks about Ukraine. Representatives from Russia, Ukraine, the U.S. and the European Union will meet Thursday in Geneva for these talks.

Russia will likely ask for a change in Ukraine's constitution, giving eastern Ukraine the right of self-government.