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BELGRADE, Serbia — Two boys have been arrested in Serbia after allegedly donning masks and storming their classroom to steal their teacher's grade book.

Police said in a statement they had apprehended Grade 7 pupils and seized a replica handgun, a knife, a balaclava cap and pair of sunglasses after the incident on Tuesday during school hours in the Belgrade suburb of Kotez.

"It appears that a third boy agreed with two friends that they would grab the grade book because of his poor grades," one police officer told Reuters.

The pair were charged with violent behavior, jeopardizing public safety and destruction and damage of property, police said.

School crime and violence have soared in Serbia since the war years of the 1990s when societies across old socialist Yugoslavia frayed under the pressure of gangsterism, corruption and nationalism.