Fierce fighting has continued between government troops and pro-Russian rebels in east Ukraine, despite renewed diplomatic efforts to enforce a truce.

Ukraine officials said six government soldiers were killed in the past 24 hours and army positions were fired on 26 times near the rebel stronghold of Donetsk. The rebels said one of their fighters was killed during attacks by the army.

On Monday, Ukraine, Russia, Germany and France called for the withdrawal of more weapons from the frontline. The four nations also expressed “grave concern” over the surge in fighting.

The statement comes after talks in Berlin between the foreign ministers of Ukraine, Russia, Germany and France.

In Berlin, the four foreign ministers called for the withdrawal of mortars and heavy weapons with a calibre of less than 100mm as well as all types of tanks.

But Germany warned that the talks had also emphasized differences over the year-old conflict in Ukraine’s Donetsk and Luhansk regions.