SLOVYANSK, Ukraine — Russia on Thursday began military drills on its border with Ukraine as the government there mobilized against pro-Russian militants, killing "up to five" people, according to Ukrainian officials.
Russian President Vladimir Putin condemned the Ukrainian actions, and his top deputies said a Ukrainian mobilization in the restive eastern part of the country would draw a Russian response. The tit-for-tat military movements brought the two sides closer to a direct armed confrontation in a standoff that analysts call one of the most dangerous on European soil since the end of the Cold War.
"If the Kiev regime has started to use the army against the population inside the country, it beyond any doubt is a very serious crime," Putin said. He added that if Ukrainian authorities escalated the confrontation, there would be "consequences."
Secretary of State John Kerry quickly denounced the Russian actions, and in unusually blunt language warned that unless Moscow took immediate steps to de-escalate the situation, Washington would have no choice but to impose additional sanctions.
"If Russia continues in this direction, it will not just be a grave mistake, it will be an expensive mistake," Kerry said in Washington.
The pro-Russian activists were killed in fighting at three checkpoints surrounding the city of Slovyansk, and one Ukrainian soldier was wounded, the Ukrainian Interior Ministry said in a statement. The violence broke out as security forces attempted to dislodge protesters and pro-Russian militants who have encamped in cities across eastern Ukraine, with other fighting reported at an arms depot and a city hall.
The Russian military launched the "tactical drills" in the regions bordering Ukraine in response to the events, Russian Defense Minister Sergei Shoigu said at a meeting in Moscow.
If Ukraine's "war machine" does not halt, Shoigu said, it will lead to a large number of casualties. "We have to react to such a development," he said.
The Russian defense minister said the drills would include aerial exercises near the border.
Information from Associated Press was used in this report.