Kiev officials blamed a dropped cigarette butt for a powerful explosion that set a chemical plant in eastern Ukraine on fire.
The huge blast on Monday triggered the blaze at the plant in Donetsk, a rebel stronghold where Malaysian Airlines flight MH17 was shot down last year.
"This was caused by a dropped cigarette butt. Accidents often happen in factories where no one is responsible for fire safety. Well, it's chaos, and they are barbarians," the spokesman said, blaming the pro-Russian rebels for the explosion.
A spokesman for Kiev's Anti-Terrorist Operation said the explosion was the fault of the rebels because of poor safety procedures,
The rebels, however, laughed at claims by Kiev officials that the explosion was set by a dropped cigarette.
The pro-Russian rebels said they were attacked by the Ukranian military and that the explosion was set by a high-calibre artillery shell from the Ukranian military.
"The explosion was caused by heavy shelling and not by cigarette butt," a rebel official told journalists.
Ukranian politician Dmitry Yarosh also claimed on this Facebook account that the area had been attacked by the military.
The blaze at the plant was also contained and controlled immediately and no longer poses danger to residents in surrounding areas, authorities said.
No one was reported killed or injured in the chemical plant fire but a heavy shelling in Donetsk recently killed two people, a rebel official said.
At least seven persons were also killed last Sunday in neighboring areas controlled by the government, the Donetsk regional police chief said.
Since the fighting between Russia-backed separatists and Ukraine government forces erupted in April, at least 5,300 people have been killed and more than a million others in eastern Ukraine were displaced, data released by humanitarian organizations showed.
In the United States, President Barack Obama held talks with German Chancellor Angela Merkel about reviving an elusive Ukraine peace plan.