A blast caused by an unidentified explosive device wounded three at a military academy in Russia's northwestern city of Saint Petersburg, the defence ministry said, RIA Novosti state news agency reported.

Servicemen at St Petersburg's Mozhaisky Military Space Academy where an explosion went off injuring several people on Tuesday. (Photo: VCG)

"An explosion of an unidentified explosive device took place around 1.30 pm (1030 GMT), in Saint Petersburg in staff premises of an administrative building at the Mozhaisky academy," the ministry said in a statement. Three people received non-life-threatening injuries and were receiving medical treatment, it added.