KANO, Nigeria (AFP) - Boko Haram fighters on Sunday launched a fresh attempt to take over the strategically crucial northeastern Nigerian city of Maiduguri, a brazen attack on a state capital just two weeks before national elections.
Losing control of Maiduguri, capital of Borno state, would be an enormous defeat for the security forces, whose handling of the six-year Islamist uprising has been fiercely criticised.
The city's fall would also likely spark a humanitarian disaster.
Four residents told AFP that Sunday's fighting began at roughly 3am (10am Singapore time) with loud explosions and gunfire, as the militants tried to enter the city from the south.
Troops backed by vigilantes have been battling the assailants for several hours, with the fighting at 9 am concentrated in the Mulai area just 3km south of the city, several witnesses said.
"The whole city is in fear," said resident Adam Krenuwa. "People are afraid of what will happen if Boko Haram defeats the security forces." The Islamist rebels tried to capture Maiduguri just a week ago, but were repelled by troops.
The military was not immediately available to comment on the latest raid.
Maiduguri's population is believed to have swelled above two million in recent weeks as residents from other parts of Borno have been forced to flee to the city to seek refuge from Boko Haram violence.
Resident Fannami Dalwaye said people could be seen fleeing towards the city from Mulai as more vigilantes were headed south to the frontline to reinforce the military.
"Some of us are in mosques praying, just waiting to hear the outcome of what happens," Krenuwa told AFP by telephone.
Nigeria's National Security Advisor Sambo Dasuki last month called for elections to be postponed.
He cited difficulties in distributing voter identity cards, but experts have questioned how Nigeria can hold legitimate national elections when significant parts of the country are controlled by Islamist rebels.
Boko Haram is believed to control at least half of Borno state, as well as several areas in neighbouring Adamawa and Yobe.
The northeast is an opposition stronghold and there are fears that the credibility of the polls could be challenged if millions of voters are disenfranchised, especially if the final tally is close.
The opposition All Progressives Congress (APC) has rejected any postponement of the vote, describing it as a stalling tactic by the ruling party which is fearing defeat after 16 years in power.
But even before the latest assault on Maiduguri, election officials conceded that voting would be impossible across much of the northeast.
Foreign observers have said that they will not even attempt to monitor polling in the region because of the unrest.
President Goodluck Jonathan, who is facing a tough challenge from former military ruler Muhammadu Buhari, has repeatedly sought to assure Nigerians that Boko Haram could be contained.
But those promises have consistently proved hollow, with the violence having escalated each year under his watch.