Ukraine said Tuesday one of its soldiers had died in a mortar fire exchange with pro-Russian insurgents near the shelled-out remains of an airport in the rebels' de facto capital Donetsk.

The sudden upsurge in violence underscored the fragility of a two-month truce that had calmed fighting after 18 months of near-constant clashes in which more than 8,000 people died.

Echoes of repeated heavy weapons fire around the western outskirts of the coal mining city -- emptied of many of its nearly one million residents -- kept many up throughout the night.

"Shells flew over our house," a resident of the nearby Oktyabrsky district who agreed to identify himself only as Sergiy for security reasons, told AFP.

"We heard mortar fire this morning. The situation has calmed down a bit and I left without waiting for the violence to resume."

It was only the fifth death of a Ukrainian soldier in combat reported by Kiev since September 1.

There have also been some civilian casualties and Ukrainian soldiers blown up by landmines that still scatter both the Lugansk and Donetsk separatist provinces.

The rebels rarely report their own losses.

"Yesterday, the positions of the Ukrainian army near Pisky and Opytne came under fire that killed one Ukrainian soldier," military spokesman Oleksandr Zavtonov told AFP.

Donetsk airport was desperately defended by a skeleton force of outnumbered Ukrainian soldiers before falling to militia fighters that Kiev claims were backed by Russian troops in January.

Moscow denies either arming or supporting the rebels and only admits to providing them with political backing at such venues as UN Security Council debates.

Yet the area remains one of the main hotspots of a devastated war zone in the once booming industrial heartland in the east of the ex-Soviet state.

Ukrainian troops and volunteer units still surround towns to the northwest of the city and the rebels occasionally fire shells and rockets at government outposts.

Both sides accuse the other of repeatedly violating the truce.

The insurgents said it was actually Kiev's forces that first opened fire on the once-gleaming international airport -- rebuilt at a cost of nearly one billion dollars (900 million euros) for the 2012 European Football Championship that Ukraine co-hosted with Poland.

"The airport has been under fire for more than an hour. They shot from mortar launchers and guns," rebel military spokesman Eduard Basurin told AFP.

But Ukrainian army spokesman Zavtonov denied the claim.

- Russia 'sabotaging' truce -

The escalation came with Kiev and Moscow envoys gathering for a new round of European-organised peace talks with the insurgents in the Belarussian capital Minsk.

The occasional meetings are meant to salvage a truce and political reconciliation agreement that Germany and France brokered between the warring sides and Russia at the same venue in February.

The 13-point peace plan was meant to resolve one of Europe's deadliest conflicts since the Balkans wars of the 1990s by the end of the year.

But that goal now seems out of reach -- an admission that French President Francois Hollande made after hosting Russian strongman Vladimir Putin and German Chancellor Angela Merkel in Paris at the start of the month.

One of the more bitter points of the sides' many disagreements involves separatist plans to stage their own elections that exclude pro-Kiev candidates early next year.

Ukrainian President Petro Poroshenko said those "fake" polls would be addressed in Minsk later Tuesday.

He also blamed Moscow for failing to pressure the militias into calling off their vote.

"The Russian side is basically sabotaging the implementation of the Minsk agreements," Poroshenko told reporters in Kiev.

"The illegal elections have not been cancelled but only postponed."