Militants blew up a boys' primary school in northwest Pakistan on Monday, the latest in a wave of attacks by Islamist extremists targeting educational institutes, local officials said. No-one was hurt in the bombing in the village of Ashraf Kalay in the Khyber tribal region, which lies between Afghanistan and Pakistan's northwest capital Peshawar, the officials said. "Militants blew up a government boys' primary school with explosives at around 3.00 am," tribal administration official Daulat Khan told AFP, adding that all seven rooms of the school were destroyed. Another local administration official, Rehan Gul Khattak, blamed the attack on the militant group Lashkar-e-Islam (Army of Islam). Lashkar-e-Islam is the main extremist group operating in Khyber, and has some ideological ties to the Pakistani Taliban. Elsewhere in the restive northwest, four suspected militants were killed in a clash with security forces in Swat valley late Sunday, the paramilitary Frontier Corps said in a statement.