Kano - 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 dead during an attempted cross-border incursion at the weekend.
But with the Tuareg people found in 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 arms are smuggled from Libya.
Security sources in Maiduguri, northeast Nigeria, say Boko Haram has for some time encouraged mercenaries 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.
"It will not be surprising at this stage," said security analyst Abdullahi Bawa Wase.
"The enlargement of the original Boko Haram with mercenaries and criminal and political elements is not in doubt."
Kyari Mohammed, a Boko Haram specialist from the Centre for Peace Studies in Yola, Adamawa state, said he, too, was not surprised at the arrival of foreign fighters.
History of violence
But he questioned how many foreign guns-for-hire had been recruited into Boko Haram's ranks, which according to one recent estimate numbered between 6,000 and 8,000 in total.
"When you are fighting this kind of war you expect the 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".
"I know that people from outside Nigeria are in this war. They are fighting us," he said earlier this year.
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.