The bus crash on the Trakia highway early Wednesday was either caused by speeding or was an asleep-at-the-wheel accident, according to Interior Minister Tsvetan Tsvetanov.

Speaking before Wednesday's regular session of the Bulgarian Council of Ministers, Tsvetanov explained that the police was working on both versions.

Transport Minister Ivaylo Moskovski, however, was adamant that the bus had been traveling within the permissible speed range.

The inspection of the burnt bus revealed a broken beam and a slashed back right tyre.

The bus had passed annual technical checkup in March 2011, during which no irregularities were found, Moskovski said, stressing that the vehicle was made back in 1989.

Acording to the records on the tachographic disc, the bus was traveling at the permissible 100 km/h.

Legal amendments forbidding the use of such outdated vehicles would have to be adopted, Moskovski stated.

The bus was made in 1989 and had last passed technical inspection on March 08, 2011 at a point of Avto Pako OOD. The next inspection was scheduled for September 07, 2011, according to the Bulgarian Transport Ministry.

The driver of the bus had passed a psychological test on May 03, 2011.