A spokesman for the North Caucasus regional emergencies center told ITAR-Tass the explosion took place about 12:20 p.m. Monday in Karata.
"Two pupils shirked classes in physical culture. Having locked themselves in an empty classroom, they closed the detonator of an explosive device to a mobile phone battery, which caused a blast," the spokesman said.
The teenagers -- both boys -- suffered wounds to their faces, hands and chests and were transported to a local hospital, the spokesman said.
"No fire followed the explosion. The building of the school was not damaged," the spokesman said.
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