etonations so powerful there were only craters left in the place of the depot

Comes two months after officials warned of serious

A series of powerful blasts at a Bulgarian explosives plant have killed 15 workers and injured three others, officials said today.

The government announced a day of national mourning for the victims of the disaster which came just two months after officials warned of serious safety breaches at the factory.

Bulgarian President Rosen Plevneliev blamed the deaths on an 'arrogant non-observance' of rules and regulations at the plant near the Serbian border.

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Distraught: Psychologists from the Bulgarian Red Cross comfort relatives of victims of the blasts at the Bulgarian explosives decommissioning plant near the village of Gorni Lom that killed 15 workers

Grief-stricken: A relative breaks down after hearing confirmation of a death of a loved one in the disaster, which came just two months after officials warned of serious safety breaches at the factory

Thirteen men and two women were killed in yesterday's blasts, said Nikola Nikolov, the head of the interior ministry's fire safety unit, after he inspected the devastated area of the plant depot.

Some managers were among the dead.

Workers had been dismantling old military mines at the site, but the exact cause of the blasts was unclear.

For safety reasons, investigators have to wait 24 hours until after the last explosion before they can enter the area.

Nikolov said the detonations were so powerful that there were only craters in the place of the depot, with debris scattered hundreds of metres away.

On standby: Bulgarian police, firemen and medics gather in a secure zone 4km from the scene of the blast. Bulgarian President Rosen Plevneliev blamed the deaths on an 'arrogant non-observance' of safety rules

Emergency: Police officers stand guard on the road to the decommissioning plant near the village of Gorni Lom

A Reuters photographer at the scene saw two weeping relatives of the victims being consoled by Red Cross workers.

'The tragedy is enormous, everything is destroyed, including the bomb shelter for the staff at the plant,' Interior Minister Yordan Bakalov said after seeing pictures taken by a drone.

The accident happened days before Bulgaria votes in a general election and at least one political party called for the vote to be postponed.

The labour ministry said an inspection of the private plant in the village of Gorni Lom, some 145km (90 miles) northwest of the capital Sofia, was carried out two months ago.

'Arrogant disregard for safety': Empty cases of ammunition are seen in a backyard of the depot. Workers had been dismantling old military mines at the site, but the exact cause of the blasts was unclear

Haphazard: Boxes for ammunition are piled up in a yard in the village Gorni Lom, where the plant is located

Inspectors had found that outdated tools were being used to dismantle ammunition and that explosives were not being stored properly, the labour ministry said.

It has now closed the plant, where 150 people worked.

Wednesday's blast followed a series of other accidents to hit the industry in recent months in the Balkan country.

Ten people were injured in August after a blast rocked a military equipment factory and in 2012, powerful explosions at an arms disposal depot in southeastern Bulgaria killed three.

'Innocent human lives were lost due to the arrogant non-observance of the recommendations and the established norms for handling explosives,' Bulgaria's president said on Thursday.