DAMATURU, Nigeria - Gunmen killed at least 40 people on Sunday in an attack on a college in northeast Nigeria, a Reuters witness said, in a region where Islamist militants have targeted schools and universities.

Islamist sect Boko Haram has intensified attacks on civilian targets in recent weeks in reaction to a military offensive against its insurgency. Boko Haram and spin-off Islamist groups like the al Qaeda-linked Ansaru have become the biggest security threat in Africa's second largest economy and top oil exporter.

Gunmen stormed the College of Agriculture in Yobe state and shot students as they slept in the early hours of Sunday, state police commissioner Sanusi Rufai said.

A Reuters witness counted 40 bodies at the main hospital in Yobe state capital Damaturu, mostly of young men believed to be students. The bodies were brought from the college, which is in Gujba, a rural area about 30 miles (50km) south of Damaturu.

Suspected Boko Haram militants have targeted several schools in recent months, including a raid which killed 27 students and a teacher at a school in Potiskum, a town about 30 miles from the site of Sunday's attack.

Thousands have been killed since Boko Haram launched its uprising against the state in 2009, turning itself from a clerical movement opposed to Western culture into an armed militia with growing links to al Qaeda's West African wing.

President Goodluck Jonathan declared a state of emergency in three northeastern state in May, including Yobe, and ordered a military offensive aimed at crushing Boko Haram's insurgency.

There was an initial lull in the violence as Islamists fled bases in cities, forests and mountains across the northeast. Then the militants began revenge attacks on schools, seen as the focus of Western-style education and culture, then on the security forces and civilians believed to be helping them.