Boko Haram bid to join ISIS a propaganda boost.

 a propaganda boost for now, but in the long term it could internationalise a conflict restricted to Nigeria for nearly six years, analysts say. 

The effort comes as both Islamic extremist groups have lost ground in recent weeks and as Nigeria's neighbours are forming a multinational army to confront Boko Haram. 

By pledging allegiance to ISIS, Nigeria's home-grown militants have severed ties to al-Qaeda, which is more powerful in the region, said Charlie Winter, a researcher at the London-based Quilliam Foundation.

Boko Haram has never been an affiliate of al-Qaeda, but its militants fought alongside al-Qaeda-linked groups during northern Mali's Islamic uprising two years ago, and some of its fighters have been trained in Somalia by al-Shabab, another group with ties to al-Qaeda, according to the group's propaganda.

Boko Haram's leader, Abubakar Shekau, reportedly pledged allegiance to ISIS leader Abu Bakr al-Baghdadi in an audio posted Saturday on Twitter. It could take three or four weeks for ISIS to formally respond, as has been the case with affiliates in Egypt, Yemen and Libya.

An alliance "would lend a more imposing quality to Islamic State with its expansionist model," Winter said. The move was symbolically "a striking development," but he doubted it would "change things on the ground in either Nigeria or Iraq and Syria”.

But "over time this pledge of allegiance might lead to the internationalisation" of a threat that until now has been mostly confined to a single region of Nigeria with occasional spillover into neighbouring countries, warned J Peter Pham, director of the Washington-based Atlantic Council's Africa Centre.

Boko Haram was little known until its April 2014 abduction of nearly 300 Nigerian schoolgirls from a school in the remote town of Chibok drew international outrage. At the time, al-Baghdadi praised the Nigerian insurgents and said the mass kidnapping was justification for the ISIS abduction of Yazidi women and girls in northern Iraq.

A partnership with ISIS could also be a recruiting tool. Fighters from ISIS franchises in North Africa who find it harder to migrate to the Middle East may choose to move to a Boko Haram emirate instead, Pham said.

The international support pouring into anti-Boko Haram forces from the United States, France, the United Kingdom and others "may render the Nigerian militants' fight all the more attractive to these foreign jihadists," Pham said.

The core of Boko Haram's estimated 4 000 to 6 000 militants is from the Kanuri tribe, which spreads across colonial-era borders in a region where people show stronger allegiance to tribes than states.

In August, Boko Haram declared it was reviving an ancient Islamic caliphate in northeastern Nigeria that spilled over those borders, in a move copying the Islamic State group. But Boko Haram's brutality, including beheadings and enslavement, predates and in some cases arguably exceeds that of ISIS, according to Pham.

Pham expects Boko Haram to engage in even more gruesome tactics if it wins the support of ISIS.

"The upcoming Nigerian elections and potential postelection upheaval provide too rich of a target environment for the jihadists to pass up," Pham said.

Nigerian President Goodluck Jonathan is running for re-election in a 28 March ballot that analysts say is too close to call and that Boko Haram has threatened to disrupt, calling democracy a corrupt Western concept.

In some ways, Pham said, an alliance could work against Boko Haram. Becoming another ISIS province could mean losing its ethnic appeal among Kanuris and its appeal among ordinary Nigerians for whom denunciations of corruption involving Nigeria's political elites resonate.

Joining ISIS would also require major strategy changes by Boko Haram that could cause friction, Winter said, explaining that Boko Haram would have to adopt the ISIS model of an Islamist utopia by providing health care and other social services taken on by ISIS in its state-building efforts.

Boko Haram has seized a large swath of northeastern Nigeria in the past eight months - an area perhaps as large as Belgium. But it has largely brutalised people who remain behind, enforcing its version of strict Islamic law by carrying out public whippings and severing of limbs of alleged transgressors.

The possibility of an ISIS-Boko Haram alliance has been on the table for months, and Saturday's pledge probably followed weeks of negotiations about how each group can benefit, Winter said.

Boko Haram may expect financial support from ISIS, which is still probably the wealthiest extremist group in the world despite recent drops in the price of oil that is the mainstay of the ISIS economy, Winter said.

More difficult would be ISIS support in training and manpower, given the geographical challenges, he said.

An alliance provides both groups with an immediate propaganda boost. Boko Haram stands to receive a new presence in social media, thanks to ISIS propagandists whose slick videos could replace Boko Haram's often incoherent and muddled messages.

And if the ISIS network of supporters start spreading Boko Haram propaganda, that will "project its influence and exaggerate its menace," Winter said.

Professor Abubakar Mustapha said just the idea of Boko Haram symbolically joining forces with ISIS enough to frighten some Nigerians.

"It will outrage and scare people," said the professor of Islamic Studies at Bayero University Kano, in northern Nigeria.