MAIDUGURI, Nigeria (AP) -- Nigerian troops Sunday repelled Islamic extremists who attacked from four fronts on Maiduguri, the biggest city in northeast Nigeria, with several civilians killed by aerial bombs and grenades and mortar shells on the ground.
Soldiers said hundreds of insurgents died.
Terrified residents fled homes shaking from five hours of heavy artillery fire and streamed in from the outskirts of the besieged city of 2 million, already crowded with another 200,000 refugees from the fighting.
In a separate attack, a suspected Boko Haram suicide bomber killed himself and eight others Sunday at the home of politician Sabo Garbu in Potiskum, in neighboring Yobe state, according to witness Abdullahi Mohammed.
Garbu is contesting a legislative seat in Feb. 14 balloting that includes a presidential election too close to call. Boko Haram denounces democracy.
For weeks Boko Haram has been closing in on Maiduguri, the group's spiritual birthplace, and if it were able to plant its Islamic State-style flag there, even briefly, it would give them a major boost as the group loses ground in remoter areas, said Jacob Zenn, author of a book about the insurgents.
Its third attack in a week on Maiduguri came as Chadian forces launched a winning offensive, acting on an African Union directive for Nigeria's neighbors to help fight the spreading Islamic uprising by Nigeria's home-grown Boko Haram extremists.
International outrage has grown over attacks across the border into Cameroon and increasing ferocity that culminated in the slaughter of hundreds of civilians in Baga on Jan. 3.
A Chadian jet fighter supported by ground troops bombed the extremists out of Gamboru and Kolfata on Saturday and from Malumfatori on Thursday, witnesses said.
Chadian troops in Kolfata were "dancing around their country's flag and chanting," farmer Awami Kolobe said, quoting refugees who returned across the border from Cameroon. The towns had been under the sway of Boko Haram for months. Gamboru is about 140 kilometers (85 miles) northeast of Maiduguri, and Baga is another 100 kilometers (60 miles) north of Gamboru, on Lake Chad, where Nigeria's borders converge with Cameroon, Chad and Niger.
African leaders at a summit Saturday authorized the creation of a 7,500-strong multinational force to fight Boko Haram.
Boko Haram warned against the coalition and said it will attack Niger, if it sends troops, just as it has attacked Cameroon, according to a message posted Sunday by the SITE intelligence monitoring service.
In Maiduguri, a senior army officer said the militants were "everywhere," attacking from all four roads leading into the city.
Another officer said hundreds of insurgents, as many as 500, were killed before they took flight Sunday and many weapons were recovered including artillery guns and rocket-propelled grenades. Both officers spoke on condition of anonymity because they are not supposed to speak to reporters.
Witnesses said some bombs launched from a Nigerian jet fighter killed civilians. Many homes were hit by bombs, including one in Zannari neighborhood that killed seven civilians, according to neighbors who requested anonymity for fear of retaliation from the military.
Ahmadu Marima said troops shot and killed five young men from a civilian self-defense group in his Abujantalakawa suburb, mistaking them for insurgents.
An elderly man and his granddaughter died when a rocket-propelled grenade exploded in their front garden, injuring a second girl, Marima said.
The government declared a state of emergency in three northeastern states in May 2013 after Boko Haram took control of dozens of villages and towns. Troops quickly drove the insurgents out but since then, ill-equipped and demoralized, have been losing ground.
In August, Boko Haram declared an Islamic caliphate and now holds about 130 towns and villages.
The uprising killed about 10,000 people last year, compared to about 2,000 in the first four years, according to the U.S. Council on Foreign Relations.
Faul reported from Dakar, Senegal.