Authorities have revoked two times the license of the ammunition factory where 15 people died after an explosion razed it to the ground, caretaker Interior Minister Yordan Bakalov revealed.

He told private national channel NOVA TV that he had managed to see with his "own eyes" both decisions of his institution dating 2010, when the previous explosion rocked the plant, and 2007, issued after an inspection.

The owners of the factor, Videx JSC, however appealed and a court overturned the rulings.

It is not yet clear which judicial institution took the step, but Bakalov stressed the Interior Ministry had sought to prevent its action by delivering a negative statement.

He refused to elaborate, but added more information will be handed out to the public after an inspection was carried out.

Labor Minister Yordan Hristoskov earlier vowed the plant would never open again, but the General Labor Inspectorate announced it would be closed down only until the reasons for the incident were established.

Meanwhile Nikolay Nikolov, who heads the Interior Ministry's Chief Directorate Fire Safety and Civil Protection, said an "unauthorized amount of materials" were in the plant at the time of the explosion, but their transfer to another location was not allowed by the ministry directorate controlling dangerous materials.

In his view, a problem with "businesses" exists, since many of them "should understand one should not only become richer, but also take preventive measures, because it was evident what a tragic outcome [lack of measures] might have".

A team of fifteen investigators and also representatives of other institutions are now entering the area around the Midzhur factory in Bulgaria's north-west, which was sealed off for 24 after the last explosion on Wednesday evening.