Tension has sharply escalated in eastern Ukraine on Thursday as Kiev resumed its military crackdown on anti-government protesters in Ukraine’s southeast and Russia responded by launching massive war games along the Ukrainian border.

Ukrainian government troops backed by armoured vehicles and helicopters on Thursday closed in on Sloviansk, a city in eastern Ukraine under full control of protesters who are demanding greater autonomy and even full independence from Kiev. 

Kiev said five gunmen had been killed when troops overran a roadblock of burning tires on the outskirts of Sloviansk. However, protesters admitted to only one killed and one wounded. 

It was not immediately clear if the security forces were going to mount an assault on the city of 1,30,000 residents or were just trying to seal it off from the rest of the rebellious Donetsk region, which is the flashpoint of pro-Russian protests in Ukraine’s southeast. 

In Moscow, Russia’s Defence Minister Sergei Shoigu announced the beginning of large-scale military exercises near Ukraine saying Moscow was “forced to react” to Kiev’s military operation against civilians.

NATO said Russia had massed some 40,000 troops on its border with Ukraine.

Mr Shoigu said Kiev had deployed more than 11,000 troops, about 160 tanks, over 230 armoured combat vehicles, 150 pieces of artillery and a lot of aviation against “just over 2,000 self-defence activists armed with 100 automatic guns captured from police and several dozen hunting guns.”

“If this war machine is not stopped today it will cause a great many dead and wounded,” Mr. Shoigu told a meeting of top Defence Ministry officials on Thursday.

Russian President Vladimir Putin warned Kiev’s authorities of “consequences” for them and for Russia-Ukraine relations over the military suppression of protests, which he condemned as a “very grave crime against the people.” 

“Crimea would have faced the same fate had we not taken measures to protest its residents,” Mr. Putin said.

Earlier this month the Russian leader admitted that Moscow had deployed troops in Crimea to prevent the pro-Western authorities in Kiev from disrupting a referendum in the region on splitting from Ukraine and re-uniting with Russia.

Kiev announced the resumption of its “anti-terrorist operation” against the protesters after an Easter break on Tuesday, shortly after U.S. Vice President Joe Biden wound up a high-profile visit to Ukraine.

Russia’s Foreign Minister Sergei Lavrov said the U.S. was “running the show” in Kiev and using Ukraine as “a pawn in geopolitical game” against Russia. 

A source in Ukraine’s General Staff told Russia’s RIA Novosti that the Ukrainian military were using NATO high-definition satellite maps for its operation in the east.

Kiev’s first attempt to suppress the revolt in the east collapsed a week ago when protesters captured six armoured combat vehicles from demoralised paratroopers. 

Protesters’ leader Vyacheslav Ponomarev, elected “people’s mayor” of Sloviansk, told Russian television on Thursday that militia would fight the government troops with whatever weapons they had.  

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