Nigerian authorities raided a bomb making factory Saturday belonging to suspected members of an Islamist sect in the northeast, the military said, after gun and bomb attacks across northern Nigeria over four days killed at least seven people.

Militant group Boko Haram is waging a low level insurgency against Nigeria's government. It used to be largely confined to its remote northeast Borno state, but this year has struck other provinces in the mostly Muslim north and the capital, Abuja.

Lieutenant Colonel Mohammed Hassan, spokesman for the joint military task force (JTF) for Borno state, said the factory was discovered in a house in the Bolori ward of the state's main city of Maiduguri.

A major factory for the production of Improvised Explosive Devices (IEDs), large quantities of unused IED materials, AK 47 rifles, ammunition and other vital items have been discovered by the JTF, he told a late Saturday news briefing.

The find came after several attacks mostly targeting security forces across northern Nigeria left a trail of dead.

Boko Haram did not claim responsibility for any of the attacks, but all bore their hallmarks, security officials said.

A bomb blast in a residential compound in Maiduguri killed at least one person and seriously wounded four others on Saturday morning, Hassan told Reuters by telephone.

Further west, in northern Kano state, gunmen opened fire on a police checkpoint in the village of Gaida Saturday, killing one policeman and wounding another, who was rushed to hospital.

Friday morning, a policeman on patrol was shot dead in Kano city, and Thursday militants attacked Kano's airforce secondary school, killing three air force officers and badly wounding a fourth, Air Commodore Ahmed Sani told Reuters.

GROWING THREAT

Nigerian security forces have seemed powerless to contain the growing threat of Islamist militants in the north, who this year struck the capital twice, including a suicide car bomb against the U.N. Nigeria headquarters that killed 26 people.

A wave of crackdowns have achieved little and in some cases their heavy handedness has radicalised the mostly poor, unemployed youths targeted for recruitment by Boko Haram.

Witnesses said a group of around 17 militants drove up in three jeeps during Thursday's attack on the air force school.

The attackers were chased away by our men. I cannot (say) who are responsible for the attack ... They are criminals carrying arms against their fellow countrymen, Sani said.

Armed men attacked a group playing a boardgames outside in Maiduguri Wednesday, leaving two dead, said witness Simon Bzigu, who escaped the raid which killed his brother.

Boko Haram, whose name translates as Western education is forbidden from the local Hausa language, has been blamed for dozens of shootings and attacks with improvised explosive devices this year.

It claimed responsibility for an attack in Damaturu, the capital of Yobe, last month that left at least 65 dead, its deadliest strike to date.

(Reporting by Mike Oboh in Kano and a correspondent in Maiduguri; Writing by Tim Cocks; Editing by Sophie Hares)