The European Union expressed fears over a spike in violence in east Ukraine that claimed 10 lives as Russia warned Kiev could be preparing a fresh offensive.
The single day death toll is the highest in over a month as government troops and pro-Moscow rebels accuse each other of gearing up for a renewed onslaught that would finish off an already tattered February truce.
"We really strongly condemn this escalation of fighting and we call all sides to cease it and to observe the ceasefire," European Commission spokeswoman Catherine Ray told journalists in Brussels on Monday.
Russia -- accused by Kiev and the West of sending troops and weapons across the border to fuel the insurgency -- turned the spotlight on Kiev, warning Ukraine could be readying for fresh fighting.
"We are concerned by the course of events in recent days which very strongly resembles the preparation for more military action," foreign minister Sergei Lavrov said.
Lavrov alleged that Ukraine's forces were intensifying their activities in Shyrokine, a flashpoint village 10 kilometres (six miles) from the government-held port of Mariupol.
Ukraine's foreign ministry, however, lashed out at the rebels and their alleged backer Moscow for the uptick in violence.
"Ukraine calls on Russia to take immediate measures to stop the escalation of the situation," the ministry said in a statement.
Civilians, soldiers dead
On the ground, Ukrainian officials reported the death of two soldiers and three civilians, while a rebel commander said five civilians were killed across the conflict zone in the latest surge in violence.
Volodymyr Kolesnyk, a spokesman for the local health department, told AFP that two civilians were killed in overnight shelling in Sartana village some two kilometres (over a mile) northeast of Mariupol.
An AFP journalist in the village saw dozens of buildings destroyed and the roof of one house ripped off."We were at home with the children when we heard the sound of a mortar," said local resident Lyubov.
"We decided to head down to the cellar but then there was an explosion."
He said one man was killed and six more civilians were wounded in a Kiev-controlled village close to the rebels' de facto capital Donetsk.
Meanwhile pro-Moscow separatist officials reported the deaths of five civilians in overnight bombardments, three of them in the city of Donetsk.
The United Nations says the conflict has cost more than 6,800 lives since April 2014 and has driven at least 1.4 million people from their homes.
Kiev's pro-Western forces in recent days have been fighting the rebels for control of a strategic highway linking Donetsk with Mariupol -- the last major government-held city in the region.
Most of the road is currently controlled by pro-Kiev units. Its capture would allow the separatist militants to step up their stop-start campaign to capture Mariupol -- a port city of nearly half a million on the western edge of the loosely defined demilitarised zone.
Mariupol's port exports most of the breakaway east's industrial output and controlling it could be a step towards creating a land bridge between the separatist region and the Russian-annexed Crimea peninsula.
In a move that further angered Kiev, Russian President Vladimir Putin visited Crimea on Monday to discuss the region's stuttering development under Moscow's rule.