Fighting flared between Ukrainian forces and Russian-backed rebels in separate parts of eastern Ukraine overnight, killing at least two Ukrainian soldiers and several civilians, Kiev's military and separatist sources said on Monday.
The clashes, near Mariupol in the southeast and at Horlivka, a rebel-held town, formed part of a resurgence in violence that further frayed a tenuous ceasefire and drove up tensions in Kiev in the run-up to celebrations for Independence Day.
Kiev accused the separatists of using howitzer artillery against civilians on the outskirts of the port city of Mariupol. In Moscow, Russian Foreign Minister Sergei Lavrov blamed Kiev for the violence, giving no detail but saying he suspected Ukraine was preparing a new offensive against the separatists.
The escalation has drawn expressions of concern from Western governments, which regard the ceasefire and tentative peace agreement worked out in Minsk, Belarus, in February as still the best chance of ending the rebellion in eastern Ukraine.
Ukrainian military spokesman Andriy Lysenko said the rebels used howitzers with a range of 15-16 km (10 miles) to shell Sartana, on Mariupol's northern edge.
"The enemy was not shelling Ukrainian positions, but a civilian town," he told a briefing. "The enemy has now adopted the tactic of firing and then quickly withdrawing. The next time they'll get a quick response. What has happened in Sartana is a challenge to our forces."
Two Ukrainian soldiers had been killed and seven wounded in attacks by separatists in the past 24 hours, Lysenko said.
Regional police said at least one man and a young woman were killed in Sartana.
"On one street there were five houses which were really badly damaged by shell fragments. One house had a well-tended garden with vines and a vegetable patch. But the house had been wrecked by shells and I saw an enormous pool of blood," a local news photographer, Mykola Ryabchenko, told Reuters by telephone.
The separatist website, DAN, said at least three people had been killed and four wounded as a result of government shelling of Horlivka, a regular front-line hot spot north of the main rebel stronghold of Donetsk.
"They were using heavy weapons. We have three men dead. Another four have various injuries," DAN quoted the separatist mayor of the town as saying.
Lysenko said the rebels had used heavy weapons including Grad rockets in attacks on government forces around Horlivka.
The upsurge in fighting dogged Russia's rouble on Monday. It touched a six-month low against the dollar, dropping 1 percent early in the session.
"We are worried by the developments in recent days which strongly recall preparation for more military action," Lavrov said, accusing Kiev of breaking terms of the truce.
U.S. Secretary of State John Kerry last week expressed "grave concern" to Lavrov over a rise in separatist attacks and urged an immediate halt to shooting.
Germany's foreign minister said the situation was explosive and he urged both parties in the conflict to come together quickly to prevent a spiral in violence.
Many artillery guns, tanks and other heavy weapons have been withdrawn by both sides under the terms of the Minsk agreement, but deaths occur regularly in sporadic outbursts of fighting.
More than 6,500 people have been killed in the conflict, which erupted in April 2014 after Russia annexed Crimea, in reaction to the fall of a Moscow-backed president in Kiev, and threw its support behind separatists in the east.
In a move Kiev was certain to see as a deliberate insult as it prepared to mark Independence Day on Aug. 24, Russian President Vladimir Putin visited Yalta in Crimea on Monday to promote tourism there, according to the Kremlin's website.
"The criminal is always drawn back to the scene of the crime," Renat Chubarov, leader of Crimea's Tatars who regard the peninsula as their homeland, said on his Facebook page.