KANO, Feb 1 (agencies): Boko Haram Islamist militants have launched a fresh assault on the strategically important Nigerian city of Maiduguri, eyewitnesses say.
Gunfire was reported on the streets of the northern city after an attack that began in the early hours of Sunday.
It comes a week after Boko Haram's last attempt to capture the capital of Borno state was repelled by the Nigerian army with heavy loss of life.
Boko Haram began guerrilla operations in 2009 to create an Islamic state.
It has taken control of many towns and villages in north-eastern Nigeria in the last year.
The conflict has displaced at least 1.5 million people, while more than 2,000 were killed last year.
Boko Haram fighters 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.
Four residents told AFP that Sunday's fighting began at roughly 3:00 am (0200 GMT) with loud explosions and gunfire, as the Islamists tried to enter the city from the south.
After heavy fighting in the Mulai area just three kilometres south of the city, troops backed by vigilantes repelled the attack, but the militants then began a separate assault to the east and gun battles were ongoing, multiple witnesses said.
"The gunmen were initially subdued in Mulai, but now they have changed strategy and are attacking through the Damboa road (to the east)," said local Bukar Mungono, in an account supported by two others. "Fighting is still going on."
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.
"The whole city is in fear," said resident Adam Krenuwa. "People are afraid of what will happen if Boko Haram defeats the security forces."
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.
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 from the Mulai area ran towards the city-centre as the violence raged earlier on Sunday.
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.