Fighting erupted overnight and in the early hours of Tuesday on the outskirts of the rebel stronghold of Donetsk in eastern Ukraine, despite an agreement reached by the Ukrainian and Russian foreign ministers a day earlier.

The year-long conflict between Russian-backed rebels and Ukrainian government forces has claimed more than 6,000 lives and left large parts of the country’s industrial heartland in ruins.

Fighting in the east had largely subsided following a ceasefire deal signed in February, but it has flared again in recent days.

Heavy shelling was heard in Donetsk late on Monday evening and in the early hours of Tuesday. Andriy Lysenko, a Ukrainian military spokesman, told a televised briefing that six troops had been killed and 12 wounded in 24 hours.

The rebels reported one fighter dead and five wounded in the overnight clashes.

The death toll is the highest since the Minsk ceasefire was signed.

Russia and Ukraine agreed in Berlin on Monday to call for the pullback of smaller-calibre weapons from the front lines of the conflict.

On the ground, however, even the previous agreement that called for a ceasefire and a withdrawal of heavy weaponry appeared to be shaky.

Lysenko also reported civilian casualties, including two teenagers wounded in shelling in the Horlivka area, north of Donetsk.

Andrei Lunev, a video journalist with the Zvezda television station was injured on Tuesday morning when he stepped on a land mine in Shyrokyne, a village on the Azov Sea that has been the epicentre of recent fighting.

Shyrokyne has changed hands repeatedly during the conflict.

An Associated Press reporter saw a column of at least 10 infantry combat vehicles moving from the rebel-occupied area on the Azov Sea coast to Donetsk on Tuesday morning.

Late on Monday, the French, German, Russian and Ukrainian foreign ministers expressed “grave concern” about violations of the shaky ceasefire, but pledged to continue dialogue.

The four gathered in Berlin to assess progress in the truce deal.

The German foreign minister, Frank-Walter Steinmeier, said the five-hour-long talks had been “very long, very intensive and at times very contentious” given the tense situation on the ground.

“We must ensure that the ceasefire is respected a lot more comprehensively than it was in recent days,” he told reporters.

In a final statement, the four ministers expressed “grave concern at the recent outbreak of fights over the last weekend”.

France and Germany said that their junior foreign ministers would continue to oversee the implementation of the Minsk accord with their Russian and Ukrainian counterparts.

“We remain committed to support the process whenever necessary,” the four ministers said.

The outcome of the talks in Berlin will be discussed at a meeting of G7 foreign ministers in the northern German city of Lübeck on Tuesday and Wednesday.