Four Ukrainian soldiers and two civilians were reported killed Friday 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 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 by pro-Russian insurgents on the airport have resulted in heavy civilian casualties caused by heavy 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.
Ukranian military spokesman Andriy Lysenko blamed the spike in rebel attacks on new supplies of weapons that he alleged they were provided by Russia under the guise of humanitarian aid.
Russia on Thursday sent its 11th shipment of trucks into eastern Ukraine that Moscow insisted were carrying winter supplies for civilians in the militia-controlled regions of Donetsk and Lugansk.
All the deliveries have been made without Kiev's agreement and have been never fully inspected by international monitors stationed on site.
"It should be stressed that the terrorists' provocations are occurring immediately after the arrival in Ukraine of (Russian) humanitarian convoys," Lysenko told reporters.
He said the latest Russian supply mission was comprised of 124 trucks.
Ukranian President Petro Poroshenko has promised to hold rare direct talks with Russia's Vladimir Putin at a January 15 meeting in the Kazakh capital Astana that would also include the leaders of Germany and France.
But both the Kremlin and German Chancellor Angela Merkel's office have said that a specific date for talks was still being discussed.Russia is expected to use the mini summit to showcase its commitment to a halt in hostilities that have already claimed more than 4,700 lives.
The warring sides agreed a reinforced truce deal on December 9 that had calmed much of violence in recent weeks.
The Kremlin 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.