SLOVYANSK, Ukraine — Defying warnings from Moscow not to confront pro-Russian militants entrenched in towns across eastern Ukraine, government forces on Thursday revived a stalled operation to regain control by force but had little to show for their efforts other than Russian military drills on Ukraine’s border and heightened alarm about Moscow’s next move.
Russia has repeatedly denied having a hand in the unrest convulsing eastern Ukraine or any intention to invade. But an announcement Thursday by Moscow that it would immediately start military maneuvers along the border with Ukraine, and a threat by Russia’s president, Vladimir Putin, of unspecified consequences as a result of what he called a “serious crime,” signaled a combustible new phase in a geopolitical battle set off by the overthrow of Ukraine’s government in February.
The day’s events also buried already feeble hopes that a deal reached last Thursday in Geneva by diplomats from the European Union, Russia, Ukraine and the United States might calm a crisis that has stirred fears of a wider conflict over control of Ukraine, a nation of 46 million that straddles a volatile fault line between Europe and Russia.
In Washington, Secretary of State John Kerry warned Russia on Thursday night that it would face additional economic sanctions if it failed to carry out that agreement. “The window to change course is closing,” he said.
On Thursday Sergei Shoigu, Russia’s defense minister, said drills would begin immediately involving troops in southern and western Russia, the areas surrounding Ukraine. The drills, which would also involve the air force, will include flights along the border, Shoigu said at a meeting of Russia’s top military council.
“We have to react to such developments,” he said of the Ukrainian attacks, declaring that Russia had a duty to stop “this military machine.”
However, the most violent Ukrainian operation on Thursday, against checkpoints north of Slovyansk, a small eastern city, raised fresh questions about the competence of Ukraine’s forces and the interim government’s thinking.
With armored vehicles and helicopter support, Ukrainian troops attacked crudely built checkpoints on a narrow access road. After a brief round of fighting, the forces — which the government said were a mix of regular infantry and Interior Ministry troops — withdrew, leaving rubble and burning tires behind.