By Tsvetelia Tsolova and Stoyan Nenov
SOFIA/GORNI LOM Bulgaria (Reuters) - A series of powerful blasts at a Bulgarian explosives plant killed 15 employees and injured three others on Wednesday night, just two months after government officials warned of serious safety breaches at the factory.
The government announced a day of national mourning for the victims of the accident at the privately-owned factory, which President Rosen Plevneliev blamed on an "arrogant non-observance" of rules and regulations.
Nikola Nikolov, the head of the interior ministry's fire safety unit, said the detonations were so powerful that there were only craters at the depot where the explosions were centred, with debris scattered hundreds of meters (yards) away.
Thirteen men and two women were killed, said Nikolov, who went with a team of mine clearance experts to search for survivors at the site in the village of Gorni Lom, some 145 km (90 miles) northwest of the capital Sofia.
Dimitar Dimitrov, 59, rushed to the factory immediately after the explosions looking for his son.
"I was the first man to enter the site after the blast. We started from here (the village), because I knew that my 26-year-old son was on a shift," he told Reuters.
"Everything there was destroyed. I am afraid ... he is gone," he said in a soft voice, overcome with grief.
Red Cross staff were consoling weeping relatives on the scene, a Reuters photographer said.
Workers had been dismantling old military mines at the factory, which employed 150 people, but the exact cause of the blasts was unclear. A thorough investigation would have to wait until investigators can enter the site 24 hours after the last explosion, for safety reasons, officials said.
"The tragedy is enormous, everything is destroyed, including the bomb shelter for the staff at the plant," Interior Minister Yordan Bakalov said after viewing pictures of the site.
At least one political party called for a general election scheduled to be held on Sunday to be postponed. Most parties canceled their final campaign rallies.
The labour ministry said an inspection of the plant two months ago found that outdated tools were being used to dismantle munitions and that the explosives were not being stored properly.
The blast follows a series of 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.
"Unfortunately this is not the first time, but yet another case which takes the lives of workers that dismantle ammunition," his statement said.
(Editing by Matthias Williams, Crispian Balmer and Sonya Hepinstall)