An explosion near a concert hall killed four people and injured 39 others in the southern Russian city of Stavropol today, with authorities saying they were probing the possibility of a terror angle into the blast.

The explosive device went off outside the House of Culture and Sports in the city, the capital of the region bordering the volatile North Caucasus.

According to the local authorities four women were killed in the blast, which took place near the hall where Caucasian dances were taught, a agency said.

The state-run Rossiya TV said that a terror angle was being probed, although the authorities have not ruled out that blast could have been triggered by business rivals as one of the cafe’s was badly damaged.

“A terrorist attack is being considered as one of the versions of what occurred,” city administration civil defense chief Boris Skripka was quoted as saying by Ria Novosti.

Stavropol lies on the north of the volatile Caucasus region, and borders on restive Chechnya and Daghestan, where frequent attacks are carried out by Chechen separatists against the security forces.

At least 50 people were killed and over 100 injured in March this year when two women suicide bombers blew themselves up at two different locations inside the Moscow Metro during the morning rush hour. The Metro bomers hailed from Daghestan.