NIAMEY: Gunmen attacked a high-security prison in Niger early on Monday in an apparent bid to free Islamist militants , but the assault was repulsed and one raider was killed, Interior Minister Mohamed Bazoum said.

Bazoum gave no details about whether anyone escaped during the attempt to lay siege to Koutoukale prison, about 50km (30 miles) northwest of the capital Niamey.

"I can confirm one dead among the attackers. He was wearing a suicide vest," Bazoum told Reuters by telephone. "The situation is now under control and our forces are combing the area to try to catch the attackers still at large.

The land-locked West African country is surrounded by unstable states, most of them struggling with Islamist insurgencies.

"We heard sustained gunfire coming from the prison just as we were going for (early morning) prayers," the director of the Koutoukale school, Abdoul Razak Ali, said by telephone.

Jihadist group Boko Haram - some of whose fighters are held in Koutoukale - has launched raids from Niger's southern neighbor Nigeria.

Militants have also crossed over from Mali to its west, and the Libyan war to its north threatens the whole region.

Bazoum said the most likely culprits for Monday's attack were the Mali-based Movement for Unity and Jihad in West Africa (MUJWA), one of a number of groups that have long operated in the largely unpoliced Sahara.

The attack came days after gunmen raided the house of a United States aid worker in central Niger, killed his guards and drove him across the desert towards Mali.

Gunmen also attacked a refugee camp earlier this month in Niger's western Tahoua region bordering Mali, killing 22 soldiers.

An Amnesty International official who visited the prison in June said it held around 550 inmates, more than double the prison's capacity, and the overwhelmed court system had too few judges to bring them to justice properly.

Most inmates were suspected members of Boko Haram, which has waged a campaign in northeastern Nigeria and also in Niger. A small number were alleged to belong to al Qaeda in the Islamic Maghreb and other militant groups, the official said.