Government troops accuse Russia-backed rebels of using heavy weapons as separatists report one fighter’s death.
One of the Ukraine’s largest munitions depots, containing more than 10,000 tonnes of munitions and missiles, went up in flames on Thursday.
The military is calling it an act of sabotage.
“A fire broke out,” said Ukraine’s Chief Military Prosecutor Anatoliy Matios. “The fire led to the detonation of munitions.”
No deaths have been reported, but about 20,000 people were evacuated from the area surrounding the depot in the eastern town of Balakliya. The town is about 150km from eastern Ukraine’s rebel-held regions.
Authorities closed off the airspace within a 40km radius of the depot. More than 600 emergency workers were also deployed.
Prime Minister Volodymyr Groysman announced that he would travel to the site of the disaster.
The munitions and arms housed in the depot were used by Ukrainian troops fighting insurgents, according to Ukrainian television.
The Ukrainian military has been battling pro-Russian separatists in the province of Kharkiv and two other eastern regions – Donetsk and Luhansk – since April 2014. The conflict has killed more than 10,000 people.
At least two civilians were killed and eight people injured in a similar incident in October 2015 in the government-held city of Svatove, near rebel-held territory.
Following Thursday’s explosion, Ukraine’s security services said they have launched an investigation.