6 Ukrainian soldiers killed in last 24 hours

Six soldiers were killed in separatist-held eastern Ukraine in the last 24 hours as fighting flared up again despite a fragile ceasefire, military spokesman Andriy Lysenko said Tuesday.

"Over the past day, as a result of serious provocations, six Ukrainian soldiers were killed, 12 wounded," he said at a news briefing.

The deaths, the highest toll in the last 10 days, come after the foreign ministers of Ukraine, Russia, Germany and France expressed "grave concern" over surging violations of a shaky February ceasefire.

The top diplomats from the four countries held talks in Berlin overnight to evaluate the status of the truce deal aimed at ending a year of fighting that has killed more than 6,000 people.

Military spokesman Lysenko said the situation in the conflict zone "remains unstable", with "armed provocations by the enemy continuing in almost all directions."

He said separatist insurgents used 120mm mortars and 122mm canons despite an agreement under the ceasefire to withdraw all such weaponry from the frontline.

Lysenko said the heaviest fighting took place around the rebel bastion of Donetsk, a city once home to a million people in the industrial east.