KIEV/MOSCOW, April 25 -- Kiev on Thursday urged Russia to pull back its troops from their joint border following Moscow's announcement of military exercises in response to Kiev's "anti-terror" operation that killed five pro-Moscow protesters.

"We demand Russia stop interference in Ukraine's internal affairs, end the constant threats and blackmail and withdraw its troops from the eastern border of our country," acting Ukrainian President Alexandr Turchynov said in a televised address.

He again accused Russia of fomenting separatist movement in Ukraine's eastern regions, saying Moscow "supports terrorists and murderers."

Moscow had begun drills near the border with Ukraine in response to Kiev's "anti-terror" operation, which left five pro-Moscow protesters dead, Russian Defense Minister Sergei Shoigu said.

"The starting gun to use weapons against their own civilians has already been fired (in Ukraine). If today this military machine is not stopped, it will lead to a large number of dead and wounded people. Nor is the situation around Ukraine being helped by the announced drills of NATO troops in Poland and the Baltic States," Shoigu was quoted by Interfax news agency as saying.

Russia has to react "to such development," the defense chief said.

Shoigu also said the air forces began forming army aviation brigades and helicopter regiments in an unprecedented manner, adding that the troops were receiving new and upgraded versions of aircraft.

Earlier in the day, Ukrainian Interior Ministry said five "separatist militants" were killed during "counter-terror" actions at three checkpoints set by a pro-Russia militia outside the city of Slavyansk.

Russian President Vladimir Putin Thursday called the operation "a serious crime," warning of "consequences" if Kiev used the army against its own people.

Using armed forces in "punitive operations" will have consequences for those who made that decision, including on the inter-state level, he warned, adding that in that case Ukraine's authorities deserved to be called "a junta" and "a clique."

Putin accused the Kiev government of exerting excessive force in dealing with federalist elements in the east of the country and of legitimizing extremist groups rather than opening up a genuine national dialogue.

"We took part in the meeting in Geneva. We signed a series of agreements there, according to which both sides were to disarm, abandon public buildings, and so on," Putin said. "We shouldn't be going down this road, but rather down the road of dialogue among all people in the country, wherever they happen to live."

Also on Thursday, Russian Foreign Minister Sergei Lavrov told reporters that the United States should use its influence to make the Ukrainian authorities fulfill their commitment to the Geneva agreement on Ukraine.

On the U.S. side, Secretary of State John Kerry on the same day accused Russia of inaction in helping to ease the tense situation in east Ukraine, warning that the United States is ready to impose additional sanctions in response.

The top American envoy alleged that Russia has refused to take "a single concrete step in the right direction" for the past seven days since the U.S., the European Union, Russia and Ukraine agreed in Geneva, Switzerland, to takes steps to de-escalate tension in east Ukraine.

He warned the "window to change course" was closing for Russia and that the U.S. was "ready to act" by imposing more sanctions on Moscow.

The Ukrainian government on Wednesday resumed its "anti-terror" operation in eastern regions after pro-Russia activists allegedly kidnapped and tortured several journalists and murdered a pro-government politician.

Kiev suspended its "anti-terror" measures last week after an agreement with Russia, the United States and the European Union in Geneva, which calls on all sides of the conflict to refrain from violence.

A new wave of unrest erupted in Ukraine's east in early April, when pro-Moscow activists seized government buildings in the cities of Donetsk, Lugansk and Kharkov.

Kiev has repeatedly blamed Moscow for inciting the unrest and splitting Ukraine, charges denied by Russia.