The death toll in Wednesday's blast near the concert hall in the southern Russian city of Stavropol has risen to five, with more than 40 people injured, authorities said.
Twenty-eight people were taken to the main regional hospital, and 10 to two city hospitals. A 17-year-old girl was taken to the city children's hospital with shrapnel wounds.
Stavropol Territory Governor Valery Gayevsky and city Mayor Nikolai Paltsev visited the site of the explosion, which occurred outside the city's House of Culture and Sport early on Wednesday evening before a Chechen band's concert.
The governor said it was likely a terrorist attack aimed at shattering national unity.
A top regional investigator, Yekaterina Danilova, told RIA Novosti the explosion was equivalent to 0.2 kg of TNT.
An investigation is underway, and the city's civil defense chief, Boris Skripka, said criminal proceedings were launched under the articles "murder of two or more persons" and "illegal circulation of explosives." The Investigative Committee said the case also came under the "terrorism" article.
The Stavropol Territory is the largest region in the North Caucasus Federal District, and hosts its administration, but has remained largely free of the violence in the neighboring republics of Chechnya, Ingushetia and Dagestan.
Chechen President Ramzan Kadyrov said the explosion was a provocation aimed to destabilize the relevant tranquility in the area.
"Some forces very much dislike that the North Caucasus is becoming a stable region attractive to domestic and foreign investors. They are trying to hinder the process in this way," he told journalists.
Terrorist attacks and militant clashes are common in Russia's North Caucasus, although the Kremlin has officially ended its military campaign to fight separatists and terrorists in Chechnya.
ROSTOV-ON-DON/STAVROPOL, May 26 (RIA Novosti)