File picture: AFP

Kano, Nigeria -

Suspected Islamist insurgents killed 29 people in Nigeria's embattled north-east, an official said on Monday, the latest carnage in a surge of violence that has left more than 100 dead this month alone.

The latest attack on Sunday hit the town of Mafa in Boko Haram's historic stronghold of Borno state, which is witnessing one of the deadliest episodes of the group's nearly five-year-old rebellion.

A security source in neighbouring Cameroon meanwhile said Boko Haram gunmen crossed the border on Sunday and clashed with Cameroonian soldiers, leaving seven dead.

In Mafa, the militants had sent fliers to the town earlier in the week to warn of an impending attack, a tactic used by the extremists elsewhere in the region, said Borno senator Ahmed Zanna.

Following the threat, some people fled, schools were closed and military reinforcements were deployed to the town, about 45km north-east of Borno's capital Maiduguri.

But when the attack began, Zana claimed that “the soldiers fled because they could not match the firepower and numerical strength of the gunmen”.

“Twenty-nine people have been buried from the attack by Boko Haram,” he told AFP.

Borno's police commissioner Lawal Tanko confirmed the latest unrest and said units were headed to Mafa to assess the damage.

Also on Sunday, Cameroonian soldiers tracked down a group of Boko Haram fighters who had crossed the border. Six insurgents and one soldier were killed.

“Around 30 heavily armed Boko Haram soldiers crept discreetly into Cameroon. A villager saw them and raised the alarm,” said Mey Aly, from a local NGO.

Such incursions from retreating Boko Haram fighters are frequent and the Nigerian government had called last week for enhanced security cooperation with Cameroon.

Information Minister Labaran Maku said: “They strike. When we pursue them, they retreat into Cameroon.”

Boko Haram's uprising, aimed at creating a strict Islamic state in northern Nigeria, has killed thousands since 2009.

Statistics have typically been hard to verify, as much of the violence has occurred in remote regions, often with poor phone access.

More than 330 people have been killed already this year - a nearly unprecedented two-month rate for the four-and-half-year conflict.

More than 800 people were killed during fierce clashes between Islamists and the police in Maiduguri in 2009.

On Saturday, 35 people died when two bombs exploded in a busy district of Maiduguri and 39 were killed about an hour later when gunmen opened fire on a nearby village with heavy weaponry.

Boko Haram previously hit targets across northern Nigeria and while the military has largely managed to contain the violence in the northeast, outrage is building in the region over the Islamists' apparent ability to attack at will and with impunity.

The governor of Borno state, Kashim Shettima, claimed last month that the military was outgunned by better-equipped Boko Haram fighters after an attack on February 15 left 106 dead.

Nigeria's military categorically denied Senator Zanna's claim that soldiers abandoned their positions.

A Mafa resident who requested anonymity said Sunday's attackers were armed with explosives, rocket-propelled grenades and lighter weapons and warned the death toll may still rise.

“Houses are still smouldering and we intend to search the debris for more bodies,” he added.

Nigeria declared a state of emergency in the north-east last May when it launched an offensive aimed at ending the insurgency.

But many believe the military onslaught has intensified the violence, with the Islamists launching waves of reprisal attacks, typically on defenceless civilians.

Boko Haram “is on a revenge mission”, the Mafa resident said, noting that many of his neighbours were still in the bush outside the town, afraid of yet another raid.

There are increasing worries of a humanitarian crisis, as people across the northeast flee their homes in fear.

The United Nations said last Thursday that 290 000 people had been internally displaced in the region between the start of emergency rule and January 1 this year.

President Goodluck Jonathan has struggled to resolve the crisis, repeatedly promising those caught up in the violence that the military strategy is working and that Boko Haram will be defeated soon.

The country's secret police announced that seven people had been arrested in connection with the death of a Muslim cleric who had previously criticised Boko Haram.

Adam Albani was gunned down with his wife and son on February 1 in the northern city of Zaria.

Analysts and Western diplomats have said improving economic opportunity in the deeply impoverished north offers the only permanent solution to the conflict. - Sapa-AFP