MOSCOW (AFP) - Two teenagers were killed in Russia's volatile Dagestan region on Wednesday when they opened a box left on the street that contained an explosive device, police said.

The explosion occurred around midday in a busy shopping area of main Dagestani city of Makhachkala, said a spokeswoman of the Dagestan interior ministry.

"Two people, teenagers, have died, and two people have been hospitalised," she told AFP.

Russian agencies quoted police sources as saying that the victims, aged 15-16, opened a box standing on the pavement outside a store, and apparently set off the bomb, which had 2kg of TNT equivalent.

Television footage showed the street with broken windows where the bomb went off surrounded by police cars and camouflaged officers with search dogs.

Dagestan is currently the most unstable region of Russia's conflict-plagued North Caucasus, with rebels staging attacks against the local authorities and police.

The region and its insurgency movement was recently thrust into the global media spotlight as it became known as the place where Boston Marathon bombing suspect Tamerlan Tsarnaev visited last year, and where his parents still reside.