Four Ukrainian soldiers and two civilians have been killed in an upsurge in mortar and rocket attacks launched just days ahead of planned international talks on the crisis.

Local authorities in the rebel stronghold of Donetsk said two civilians were killed and seven injured in clashes on Friday around the industrial city's disputed airport.

The air hub - once the busiest and most modern in the largely Russian-speaking east of Ukraine - has been held by a skeleton force of government soldiers since late May.

Almost daily attacks on the airport by pro-Russian fighters have resulted in heavy civilian casualties caused by intense rocket fire from both sides going astray.

The Ukrainian military said four of its soldiers had also been wounded in the past day of violence around the separatist province.

Rare talks

Ukranian President Petro Poroshenko has promised to hold rare direct talks with his Russian counterpart Vladimir Putin at a January 15 meeting in the Kazakh capital Astana, that would also include the leaders of Germany and France.

The Kremlin and German Chancellor Angela Merkel's office have said that a specific date for talks was still being discussed.

The warring sides agreed a reinforced truce deal on December 9 that had calmed much of violence in recent weeks.

Russia denies Ukranian and Western charges of backing the eastern uprising in order to throw off balance the pro-European leaders who replaced a Moscow-backed president in the wake of a popular uprising in February.

Source: Agencies