A bomb exploded Wednesday on a bus in Tolyatti, Russia, killing eight people and injuring about 50 other.

The explosion was caused by a four and a half pound explosive device, according to Irina Doroshenko, a spokesperson of the local investigative prosecutor’s office.

The attack is thought to be a terrorist one according to Vladimir Artyakov, governor of the Samara Region. Apparently, a passenger was carrying the bomb and accidentally detonated it. It is known that Tolyatti is a centre of organized crime.

The persons traveling in the bus were mostly students, according to media reports. The attack happened around 8 a.m. at the intersection of Marx and Gagarin Streets. The windows from the first and second floor of a building were shattered.

According to the New York Times, press secretary for the Tolyatti Department of Health, Olga Yevtushevskaya said: “If the bus would have driven any further it would have blown up in front of a school, which would have been a catastrophe.”

She also said that five people were seriously injured, having severe burns. Among the injured were also three children.

This was the second blast in one week that occurred in Russia. The first occurred when a woman that was on a minibus in Dagestan detonated the grenade she was carrying. Investigators called it an accident.

Politicians speculate that this was an attempt to emerge social unrest. The head of the country’s main security agency warned at the beginning of fall of some pre-election violence and said that the security would be severe before the elections on December 2.

In 1999, before national elections, explosions occurred in several residential buildings in Moscow and other Russian towns, generating many casualties. Kremlin critics and opposition activists accused the government of using the explosion as a motive to send federal troops back to Chechnya.