Boko Haram attacks targeting airport and air force base prompt 24-hour curfew in Maiduguri, Borno state

Overnight attacks by Boko Haram Islamists forced authorities on Monday to impose a 24-hour curfew in Maiduguri, northeast Nigeria, closing the airport and shutting roads into and out of the city.

The government in Borno state said the decision was taken after consultation with the military, which is believed to have been the target of the strikes by hundreds of militant fighters.

"The imposition of the curfew is necessitated by an attack in Maiduguri by people suspected to be Boko Haram members in the early hours of today," said state government secretary Baba Ahmed Jidda.

The apparently large-scale attack in a major urban centre will cast further doubt on military claims that Boko Haram, which was last month designated a terrorist group by the United States, has been pushed into remote areas.

At the weekend, the military said they would tighten security in communities near Nigeria's northern and eastern borders with Chad, Niger and Cameroon due to fears about Boko Haram strikes over the Christmas and New Year period.

Army spokesman Ibrahim Attahiru said on Monday that one of the attacks struck near the city's airport but he was not able to provide further details, amid reports that the airport and a nearby air force base were targeted.

The phone network has been down in Borno since mid-May, when the government imposed a state of emergency in the state and two others in a move designed to block militants from co-ordinating attacks.

Details of the ongoing conflict have been difficult to verify because of the communications black-out.

The latest violence began at around 3:00 am (0200 GMT) and included bomb and gun attacks, said an AFP correspondent in the city, where Boko Haram was founded more than 10 years ago.

"They entered Maiduguri from the bush, chanting 'Allahu Akbar' (God is great)," said one Nigerian intelligence officer, adding that some insurgents had been detained, without specifying numbers.

Ambulances were seen moving out of the air force base and the adjoining Ngomari neighbourhood and  roads in the city were deserted.

Local residents said there had been fatalities but there was no immediate confirmation.

The insurgents were also said to have ambushed military checkpoints around Njimtilo, on the outskirts of the city.

The state government's Jidda called for residents to remain "calm and law-abiding until the situation is put under control, as the security agencies will do everything possible to maintain lives and property of the citizenry".

He added: "Only vehicles on emergency call and essential services are allowed to move during the period. The curfew would be lifted as soon as the situation improves."

Monday's attacks come after suspected Boko Haram militants killed 24 people in two separate strikes in Borno state on Saturday and last Thursday.

Seven fishermen were ambushed and killed in the first attack in Baga, a fishing community on Lake Chad, where nearly 200 people, including soldiers, insurgents and civilians lost their lives in fierce fighting earlier this year.

Seventeen others were killed in the second attack, when gunmen in pick-up trucks torched more than 100 shops and vehicles in the Sabon Gari area of Damboa district, 90 kilometres (56 miles) from Maiduguri.

Boko Haram, whose name translates from the Hausa language of northern Nigeria as "Western education is sin", wants to impose a strict form of Islamic law or sharia in the region and has been blamed for thousands of deaths since 2009.

Last Friday, Human Rights Watch called on it to stop targeting ordinary Nigerians, claiming it was conducting reprisal attacks on the wider public in retaliation for intelligence passed on to the military by civilian vigilantes.