Government forces are reporting gains in rebel-held eastern Ukraine as the parties in the conflict gear up for talks.

Fighting between government troops and Russia-backed separatists has killed more than 5,300 people since April, according to the U.N.

The volunteer Azov battalion said on social media on Tuesday that it captured several villages north-east of the strategic port of Mariupol, pushing the rebels closer to the border with Russia.

Rebels reported advances, too. Their military spokesman Eduard Basurin said late Monday that they have surrounded the railway hub of Debaltseve, the focus of fierce fighting in the past weeks, cutting it off from a major highway.

Representatives of Ukraine, Russia, rebels and the Organization for Security and Cooperation in Europe are meeting for long-anticipated talks later on Tuesday.