The militants locked the main gate of Ram Krishna Higher Secondary School at Ghari area on the outskirts of the capital yesterday but the lock was broken by angry local residents.
Officials and people of the state have appealed to the militant outfits not to disturb the academic atmosphere in the state.
Sources said different militant outfits have been hurling bombs and grenades at school complexes in various parts of the state particularly in four valley districts of Imphal East, Imphal West, Bishenpur and Thoubal for failure to meet their monetary demands.
"How can the school authorities pay such a huge demand," he said, adding that the school was set up some years ago to cater to the needs of poor rural students.
Students and teachers, who arrived at the school yesterday morning, organised a sit-in at the nearby community hall and appealed to the militants not to disturb the smooth functioning of the school.