On Thursday, the Bulgarian government released what little was known about at factory explosion in a northwestern city the previous night.

The fatal accident occurred at a facility used for decommissioning landmines and dismantling obsolete ammunition. It remains unclear what caused the blast.

Civil defense force director Nikolai Nikolov confirmed that all employees known to be at the factory at the time of the incident had been killed.

"Thirteen men and two women perished. The blast was so powerful that it left craters," Nikolov said.

Three people in the nearby vicinity also sustained injuries.

The secretary-general of Bulgaria's interior ministry, Svetlozar Lazarov, described the site as having "been reduced to ashes," when he spoke to reporters on Thursday.

The explosion occurred in the town of Gorni Lom, which is located roughly 120 kilometers (75 miles) northwest of the capital city, Sofia.

kms/mkg (AP, AFP, dpa)