Islamabad, Pakistan (CNN) -- Militants planted explosives in a boys' school in Mohmand Agency on Sunday, bringing to 40 the number of schools they have destroyed in the area, authorities said.
No one was hurt in the latest attack.
Mohmand is one of seven semi-autonomous tribal agencies along the 1,500-mile porous border that Pakistan shares with Afghanistan
In the Sunday attack, unidentified militants planted explosives in three of the 11 rooms of the school in the Lakaro subdivision of Mohmand, said Maqsood Khan, an area official.
All three rooms were damaged by the blast.
Khan said the attack is the 40th at a school in the area.
The bombing is the latest in a spate of attacks on schools in Pakistan. They are usually carried out in the middle of the night when schools are empty.
Early Saturday, militants blew up a boys' elementary school in the Cherah Gali area of North West Frontier Province. The three-room structure was empty at the time.
Journalist Nazar Ul-Islam contributed to this report.