The United States on Thursday said it was concerned by increasing Boko Haram violence and territorial gains in Nigeria, warning that the deteriorating situation threatened the African giant's future.

Boko Haram, which has been waging a violent insurgency that has claimed thousands of lives since 2009, has in recent weeks overrun and held swathes of territory in Nigeria's far northeast.

Nigeria and its regional allies on Wednesday called for greater international support to shut down Boko Haram's weapons and funding supply as concern mounted at the group's rapid recent land grab.

The call came after conflicting reports that the militants had seized another town, prompting warnings that Nigeria was losing control of the northeast and violence could spill across borders.

Foreign ministers from Nigeria and neighboring countries met on Wednesday to discuss Boko Haram, as the militants' rapid land grab intensified in the far northeast, raising fears for regional security.

Cameroon's army claimed on Tuesday to have killed more than 40 Boko Haram fighters who tried to storm a strategic border crossing from Nigeria.

Heavily armed fighters "attempted to cross the bridge at Fotokol" in the extreme north of the country and opened fire on Cameroonian soldiers, the ministry of defense told state radio. 

Boko Haram insurgents have reportedly taken over the town of Bama in northeast Nigeria's Borno state, following heavy fighting with government troops, but the military disputed the claim.

Scores of Boko Haram militants on Monday launched pre-dawn attacks on troops that had deployed in the town in preparation for a large-scale offensive to reclaim territory seized by the Islamists.

Nigeria faces an open-ended fight against Boko Haram unless it changes its approach to ending the insurgency, according to a new research paper published on Tuesday.

Marc-Antoine Perouse de Montclos, from the French Institute of Geopolitics in Paris, said the military and political response had to change and that "years of mishandled responses" had effectively fueled the violence.

Boko Haram militants on Monday launched a pre-dawn raid on Nigerian troops as they prepared for a major offensive to retake a town that the group's leader declared part of his Islamic caliphate.

Scores of Boko Haram fighters stormed the town of Bama as soldiers readied for an attack on the nearby town of Gwoza, which was seized by the Islamists on August 7.

Boko Haram gunmen have killed scores of residents in a Nigerian town on the border with Cameroon that they captured in recent raids, witnesses told AFP on Saturday.

The militants seized Gamboru Ngala earlier this week after taking over military and police facilities in a fierce gun battle which forced thousands of residents across the border into Cameroon.

At least 10 people died in Nigeria on Friday when a boat carrying 35 passengers bound for Port Harcourt capsized and sank, a rescue official and local government spokesman said.

"We can confirm that 10 persons died early today when a Port Harcourt-bound passenger boat sank," National Emergency Management Agency (NEMA) co-ordinator Onimode Bandele told Agence France Presse.

Cameroon's army has attacked the Nigerian Islamist group Boko Haram, shelling one of their camps across the border and killing "many" fighters, a security official said on Thursday.

The source said the army had shelled the camp on Wednesday evening, two days after the jihadist group had seized control of the town of Gamboru Ngala on the border with Cameroon.