Nigeria and its neighbours agreed on Thursday to set up a joint military force to counter Boko Haram, a sign of President Muhammadu Buhari's intent to crush the Islamist militant group early in his tenure.

At a one-day summit at Abuja airport, the 72-year-old former military ruler, who was inaugurated just two weeks ago, welcomed the leaders of Chad and Niger, and the defence minister of Cameroon.

A statement afterwards said the joint force, based in the Chad capital Ndjamena, would be up and running by July 30 with a permanent Nigerian leader, a concession to Buhari's opposition to rotating commanders.

Changing the force's leadership would hamper "the military capacity to sustain the push against the insurgents, who also have the uncanny ability to adapt and rejig their operational strategies", Buhari said before the meeting.

Chad and Cameroon have deputy commander and chief of staff posts in the force, whose mission is to crush Boko Haram, which has killed thousands and displaced 1.5 million people in its six-year fight to establish an Islamic state in Nigeria's northeast.

Quelling the insurgency was one of Buhari's main campaign promises, in contrast to his predecessor Goodluck Jonathan, who was accused of dithering and incompetence, particularly after the kidnapping of more than 200 girls from a school in the town of Chibok in April last year.

CRACKS

In his two weeks since assuming office, Buhari has focused on little else, traveling to Niger and Chad and shifting the military command center from Abuja to Maiduguri, the capital of northeast Borno state and birthplace of the insurgency.

In his absence, cracks have started to emerge in his All Progressives Congress (APC), a loose alliance of powerful Nigerians with little binding them together apart from a shared desire to eject Jonathan's People's Democratic Party (PDP) from power.

Buhari, an ascetic northern Muslim, has named Yemi Osinbajo, a southern Christian lawyer from Lagos, as his vice president but has failed to give any clarity on his eventual cabinet line-up.

Although such delays are common in Nigeria's convoluted politics, analysts say it suggests disagreements and horse-trading between Buhari and Bola Tinubu, the Lagos political godfather who provides much of the APC's muscle.

In another early setback for Buhari, his choice for Senate president – the third most important position in the country – failed to win election after party rival Bukola Saraki broke ranks and secured enough PDP support to secure victory.

Saraki's move provoked markedly conflicting responses from the APC.

"The president took the view that a constitutional process has somewhat occurred," Buhari spokesman Femi Adesina said, a comment at odds with party spokesman Lai Mohammed, who accused Saraki of "the highest level of indiscipline and treachery".