The fighting broke out shortly after President Petro Poroshenko declared an end to a 10-day cease-fire and ordered government forces to renew their effort to put down the pro-Russia separatist insurrection in the east.
Poroshenko’s announcement, in a nationally televised statement after midnight, came after two days of conference calls with the leaders of Russia, France and Germany that failed to yield concrete steps toward a peace agreement.
On Friday, European leaders issued an ultimatum to Russia, demanding it do more to end the violence in eastern Ukraine.
But attacks on government forces continued.
At least 27 Ukrainian soldiers have been killed in clashes with rebels since Poroshenko announced the unilateral cease-fire on June 20, and he had come under heavy political pressure to resume military action against the rebels, whom the government and many Ukrainians regard as terrorists.
There were reports of heavy shooting and bombardments all across eastern Ukraine on Tuesday, with civilian casualties.
In the city of Kramatorsk, four people were killed when a minibus was hit by artillery fire, Ukrainian news agencies reported. In a strategic victory for the government, Ukrainian forces retook control of a border checkpoint at Dolzhanksy, one of three important border crossings with Russia that had been seized by rebels.
Rebels, meanwhile, said they had taken full control of the main airport in Luhansk, where a military transport plane was shot down last month, killing all 49 soldiers aboard.
In Donetsk, the capital of Ukraine’s eastern industrial heartland, rebels seized control of the headquarters of the regional Interior Ministry, leaving the body of a plainclothes police officer outside.
Russian President Vladimir Putin condemned Ukraine’s renewed use of military force.
“Unfortunately, President Poroshenko has resolved to resume military action,” Putin said at a meeting of Russia’s ambassadors in Moscow.
“We failed to convince him that the road to a secure, stable and inviolable peace cannot lie through war.”
Ukrainian officials have accused Russia of publicly pushing peace while allowing weaponry and volunteers to flow over the border into eastern Ukraine, a charge the Kremlin has denied.
Many of the key separatist leaders in Ukraine are Russian citizens, and rebels have said they have used advanced Russian-made shoulder-mounted rockets to shoot down Ukrainian military aircraft.
Putin stopped short of committing Russia to any specific response to the renewed violence, but he stressed that he would defend any threat to Russians anywhere.
He accused the United States of stoking tensions in Ukraine and campaigning in Europe to turn countries against him, calling sanctions against Russia “blackmail.”
“This country will continue to actively defend the rights of Russians, our compatriots abroad, using the entire range of available means — from political and economic to the right to self-defense envisaged by international humanitarian law,” he said.
The Kiev government and self-appointed separatist leaders met for their first talks last week, with former President Leonid Kuchma representing Poroshenko in the negotiations.
Poroshenko has offered guarantees on Russian language and increased autonomy to eastern Ukraine as concessions to residents there, but neither side appeared prepared to yield enough ground.
Separatists said Tuesday that they would be willing to return to the negotiating table only if security forces pulled out of eastern Ukraine — a demand that would effectively concede the independence of the regions and one that Poroshenko has ruled out.
Last week, European Union leaders gave Russia a Monday deadline to push rebels toward handing over control of the border to Ukraine and to negotiate with Poroshenko, hinting that new sanctions would soon follow otherwise.
EU ambassadors met in Brussels on Tuesday but made no announcement about further punitive actions against Russia.
The turmoil in Ukraine was set off in November when Russia-friendly President Viktor Yanukovych abandoned plans to sign an EU trade deal, sparking months of protests and his ouster in February.
Russia quickly moved to annex Ukraine’s autonomous Crimean Peninsula, and U.S. and NATO officials have accused Moscow of stoking separatist sentiments in the east.