YAOUNDE (AFP) - A 12-year-old girl suicide bomber killed 20 people in an attack on a bar in Maroua in Cameroon, while in a crowded market in neighbouring Nigeria a "mentally handicapped" female attacker killed 14.

The child bomber blew herself up among Saturday night revellers in the popular bar, injuring at least 79 others, Cameroonian state TV reported on Sunday.

Early Sunday, in the northeastern Nigerian town of Damaturu, a woman described by locals as "mentally unstable" detonated herself at the entrance of a market, trader Garba Abdullahi told AFP.

There was no immediate claim of responsibility for either bombing, but Nigeria and increasingly Cameroon have suffered repeated attacks by Boko Haram extremists, including a recent string of suicide attacks by women and girls.

The Islamists, whose six-year insurgency and efforts to quell it have left at least 15,000 dead, have recently stepped up their attacks in the restive Lake Chad region despite a major regional offensive.

Cameroon's army has joined the campaign against Boko Haram after a series of deadly cross-border raids into its territory.

The insurgents have abducted thousands of people, including hundreds of women and girls, in the past two years, rights groups say.

The former commercial hub of Maroua in northern Cameroon was already reeling after 13 people were killed in twin suicide bombings by two teenage girls on Wednesday in a central market and in a nearby neighbourhood.

Violence returned on Saturday night to the town, which has been under heavy security for months as the threat from Boko Haram has grown.

"A girl of around 12 blew herself up between two takeaway sales points. Security forces have sealed off the area and have made several arrests," state TV said.

Saturday's was the fifth suicide attack to hit Cameroon in two weeks.

A resident told of "a loud explosion", saying there had been an attack at the Boucan bar, a large and popular nightspot.

"There's panic," he said.

Motorbikes, which the insurgents often use to stage their raids, are banned in Maroua after dark, and several regions of Cameroon have prohibited the use of the full Islamic veil as they seek to curb the threat from female suicide bombers.

WAVE OF VIOLENCE

In Damaturu in Nigeria, witnesses and hospital sources described the tragedy that struck the market area on Sunday.

"Today is the market day here and at 9.50 this morning, a female suicide bomber blew herself up at the... entrance of the market where commuters were arriving," trader Abdullahi told AFP.

"We evacuated 15 dead bodies to the hospital, including the suicide bomber who was identified as a mentally unstable woman that had been known for years in the area," he said, adding that the attacker was around 40 years old.

The death toll was confirmed by a nurse from a local hospital, who added that 47 people with injuries - many of them critical - had been admitted.

"Eight of the dead are women. One of them, from all the indications, was the suicide bomber," added the nurse from the Sani Abacha Specialist Hospital, who requested anonymity.

Dumaturu was the scene of a triple suicide bombing on July 18 when three girls blew themselves up killing at least 13 people as residents prepared for the Muslim Eid festival marking the end of Ramadan.

The town is the capital of Yobe state which, along with the other northeastern states of Borno and Adamawa, has been the worst hit by Boko Haram's bloody campaign for a hardline Islamic caliphate, which has left 1.5 million people homeless since 2009.

A new wave of violence has claimed 800 lives since Nigeria's President Muhammadu Buhari came to power in May vowing to crush the insurgency.