(Reuters) - A new round of peace talks were about to start on the Ukraine crisis on Saturday, even as fighting between Kiev government forces and pro-Russian separatists raged in the east, claiming civilian and military lives.

A Reuters reporter in the Belarussian capital saw the main participants in the so-called 'contact group' -- including Ukrainian former president Leonid Kuchma, a Russian diplomat and rebel officials -- arrive at Minsk airport and then drive off towards the city.

The talks, under the auspices of the Organization for Security and Cooperation in Europe (OSCE) whose official also arrived in Minsk, will be the first since September when a ceasefire was agreed.

Much-violated from the start, that truce collapsed completely as the rebels launched a new advance last week.

Heavy shelling continued in Ukraine's eastern regions as the separatists sought to tighten a circle around government forces clinging on to control of the strategic rail and road junction of Debaltseve.

Regional police chief Vyacheslav Abroskin, in a Facebook post, said 12 civilians had been killed on Saturday by separatist artillery shelling of the town, which lies to the north-east of the big city of Donetsk.

Defense Minister Stepan Poltorak said 15 Ukrainian soldiers had been killed and 30 wounded in clashes across the east.

"The toughest situation is in the Vuhlehirsk area where the terrorists are trying to seize the town and occupy positions to move forward and encircle Debaltseve," military spokesman Andriy Lysenko said in a separate briefing.

Debaltseve is located on the main highway linking Donetsk and the other big rebel-controlled city of Luhansk and is also a vital rail link for goods traffic from Russia which Kiev accuses of arming the rebels.

The rebels were also continuing to threaten Mariupol, a town of half a million in the south-east of the country on the coast of Sea of Azov, Lysenko said.

The renewed violence followed intense fighting on Friday in which more than 20 civilians were killed in separate shelling attacks in Donetsk, Debaltseve and other areas.

More than 5,000 people have been killed in the Ukraine conflict which erupted last April following Russia's annexation of Crimea in response to the ousting of a Moscow-backed president in Kiev by street protests.

The West and Kiev's pro-Western government say Russian regular forces are fighting on behalf of the separatists and providing them with military equipment through the long joint border, parts of which are beyond Ukrainian control. Moscow denies this.

U.S. and Western sanctions against Russia have led to the biggest crisis in Russia-West relations since the end of the Cold War more than 20 years ago.

(Additional reporting by Natalia Zinets)