Nigeria: Cameroon's claims this week that two Tuareg fighters were among the dead when troops bombarded Boko Haram positions have sparked fresh interest in the group's links to the wider jihadi network.
Communication minister Issa Tchiroma Bakary did not elaborate on the nationality of the foreigners, who were among the more than 100 killed during an attempted cross-border raid at the weekend.
But with the Tuareg spread across Mali and Algeria, which are both home to Islamist groups, the claim is coming under close examination.
Boko Haram was designated an Al-Qaeda-linked terror group earlier this year while its recent land grab in Nigeria's northeast has prompted comparisons to Islamic State militants in Syria and Iraq.
Analysts remain sceptical, though, about the extent of its direct operational links with outside groups, despite claims that some fighters were trained in Mali and that arms are being smuggled from Libya.
Andrew Noakes, co-ordinator of the Nigeria Security Network of analysts, said it was "plausible" that Boko Haram had fighters from beyond the lands populated by its Kanuri tribal base.
"There is most likely a relationship of convenience between Boko Haram and AQIM (Al-Qaeda in the Islamic Maghreb), which may stretch to sourcing militants from outside the insurgency's traditional area of recruitment," he told AFP by email.
"But we should retain a healthy degree of scepticism about the particular claim of Tuaregs fighting with Boko Haram."
Hired mercenaries
Security sources in Maiduguri, northeast Nigeria, say Boko Haram has hired mercenaries for some time from neighbouring countries such as Chad, Niger and Cameroon.
"These fighters are paid allowances after every raid, which ranges between 50,000 naira ($300) and 150,000 naira for each fighter," the source told AFP in a recent interview.
Others said the recruitment was to be expected, given the increase in violence this year that has left thousands dead and prompted hundreds of thousands of civilians to flee.
But Kyari Mohammed, a Boko Haram specialist from the Centre for Peace Studies in Yola, Adamawa state, said he questioned how many foreign guns-for-hire had been recruited.
"When you are fighting this kind of war you expect an influx of mercenaries, especially in this region where we have porous borders and a history of violence," he said.
"There could be infiltration of mercenaries across these borders but not on a huge scale."
'Al-Qaeda in west Africa'?
Nigeria's President Goodluck Jonathan has described Boko Haram as "Al-Qaeda in west Africa" and has been keen to play up a regional dimension to the five-year insurgency.
Chief of Defence Staff Alex Badeh has said weapons recovered during operations were "very alien to Nigerian armed forces, which means there are people from outside fuelling this thing".
But some analysts see Nigeria's position as a way of deflecting criticism its own role in transforming a largely peaceful domestic anti-corruption movement into a heavily armed terror group.
Boko Haram gained a higher international profile in April this year when it abducted more than 200 schoolgirls from the remote northeastern town of Chibok.
The United States said last week that it was concerned by its capture of a succession of towns and the potential for a humanitarian crisis.
Despite that, security experts say the conflict remains largely an internal domestic issue and that Boko Haram has localised aims.
Others point out that forced conscription of young men from across Nigeria's borders could also explain the presence of foreign nationals to boost Boko Haram's depleted ranks.
In Cameroon, young men from towns and villages near the Nigerian border have been conscripted with inducements of motorcycles and 150,000 naira in cash as a "signing-on fee", the security source in Maiduguri added.
Police in Cameroon's impoverished far north region confirmed to AFP in August that hundreds of young people had been forced to fight.
"Children from Kolofata were conscripted, drugged, manipulated and sent against their own city," one police officer said.
