MAIDUGURI, Nigeria (AP) -- Islamic extremists attacked Maiduguri, the biggest city in northeast Nigeria from four fronts overnight with the crescendo of warfare - booming cannon and whooshing rockets - continuing Sunday, witnesses said.
The third attack in a week on Maiduguri comes amid unconfirmed reports that a Chadian jet fighter helped bomb the extremists out of Gamboru on Nigeria's northeast border with Cameroon. Boko Haram insurgents had held the trading center since August.
Chadian forces on Thursday liberated Malumfatori, another border town that was under the sway of Boko Haram for months.
African leaders at a summit Saturday authorized the creation of a 7,500-strong force from Nigeria and its four neighbors to confront the spreading Islamic uprising by Nigeria's home-grown Boko Haram group.
Trapped residents in Maiduguri said they could not sleep for the noise from cannon, rockets and submachine gunfire that began Saturday night.
A senior army officer said the militants were "everywhere," attacking from all four roads and were within 15 kilometers (10 miles) of the city of 2 million. The officer spoke on condition of anonymity because he is not allowed to give information to reporters.
All exits are blocked and Maiduguri's international airport has been closed since the insurgents launched a major attack in December 2013 and destroyed five aircraft at a neighboring air force base.
Maiduguri is the birthplace of the extremist movement.
Nigeria's President Goodluck Jonathan declared a state of emergency in May 2013 when he admitted Boko Haram had taken control of dozens of northeastern 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, according to Amnesty International.
The extremists have increased the tempo and ferocity of attacks. About 10,000 died in the past year compared to about 2,000 in the first four years of the uprising, according to the U.S. Council on Foreign Relations.
Jonathan is running for re-election in a tightly contested Feb. 14 vote. Boko Haram denounces democracy as a corrupt Western invention.