A suicide bomber struck a crowded market in the northeastern Nigerian city of Maiduguri on Friday, killing six people, the national Emergency Management Agency (Nema) said, in an attack that bore the hallmarks of Islamist militant group Boko Haram.

There was no immediate claim of responsibility for the blast, but Maiduguri, the capital of Borno state, has been often been targeted by Boko Haram in its campaign to carve out an Islamic "caliphate" in Nigeria's northeast.

Eleven people were wounded in the attack, the latest in a spate of bombings and shootings that have killed more than 600 people across the north, according to a Reuters tally, since President Muhammadu Buhari was inaugurated on May 29.

Witnesses said the driver of a motorised rickshaw detonated a device at the entrance to the crowded market around 7.30 am (0630 GMT).

"The wreckage of the tricycle used by the bomber was there. I saw the charred body of the bomber," said Usman Ali, adding that he saw rescue workers removing bodies from the scene.

The market is in a district of Maiduguri that was controlled by Boko Haram for just over a year until late 2013 when grassroots security groups set up by local residents ousted the jihadist militants.

Boko Haram held a northeastern area around the size of Belgium at the end of 2014 but the Nigerian military says it has since wrested back much of this territory with the help of armed forces from neighbouring Chad, Niger and Cameroon.

Buhari transferred the headquarters of military operations against Boko Haram to Maiduguri from the capital Abuja, outside the main northeastern conflict zone, shortly after his inauguration. Boko Haram has since stepped up guerrilla-style attacks in the north and neighbouring states.

An 8,700-strong task force of troops from Nigeria, Cameroon, Chad, Niger and Benin was due to start operations against Boko Haram on Friday but has been dogged by a lack of funding and political resolve.

In a move toward activating the force, Nigeria announced on Thursday the appointment of Major General Iliya Abbah as its commander, but significant military operations appear unlikely before the end of the rainy season in September. - Reuters