By David Lewis
DAKAR (Reuters) - The bombing of a U.N. office in Nigeria has deepened fears that al Qaeda's influence on militant groups in sub-Saharan Africa is growing, although the extent of its involvement remains murky.
Experts say increasing numbers of Nigerians are training with fighters linked to al Qaeda in the desert, potentially adding black African recruits to ranks still mostly dominated by Arab faces, and broadening al Qaeda's regional influence.
Sharing men and ideas is not new -- Islamists from North Africa flooded to Iraq to take part in the insurgency there, with many having since returned back home.
But evidence is emerging that al Qaeda may be broadening its reach south, possibly by sharing training, tactics and weapons, with other militant groups, after failing to strike in Europe and facing heavy resistance in Algeria.
The United States, United Nations and the European Union have also expressed concern that al Qaeda fighters in the Sahara may be acquiring weapons looted from former Libyan leader Muammar Gaddafi's stocks.
The Nigerian Islamist sect Boko Haram, which claimed the August 26 Abuja bombing, and al Qaeda's North African wing AQIM which emerged from Algerian militant groups and now roams across much of the Sahara, appear awkward bedfellows due to traditional tensions between black and Arab Africans.
"(But) the links between Boko Haram and AQIM are there and probably getting stronger," said a diplomat who follows security issues closely but asked not to be named.
"We are not clear on the degree of cooperation. But if you are training people you are going to be talking about strategy, so there is a degree of coordination," the diplomat added.
Nigerian authorities said last week they suspected a member of Boko Haram "with al Qaeda links" who returned recently from Somalia to have been involved in the bombing that killed 23.
The bombing was a clear escalation in targets and methods for a group that rejects Western education but previously targeted security forces in the poor, marginalized Muslim north.
It also mirrored al Qaeda's bombing of U.N. headquarters in Iraq in 2003 and another in Algeria in 2007.
Kwesi Aning from the Kofi Annan International Peacekeeping and Training Center said that the apparent convergence of at least some of the groups' interests was a significant concern.
"It changes the equation totally," he said.
Any potential links have not come out of the blue. Al Qaeda offered Boko Haram help last year to fight Christians.
Citing the lack of open-source proof on collaboration and ethnic differences between the groups, most analysts have tended to remain cautious over any kind of alliance.
"Although AQIM has expanded into sub-Saharan Africa, there remains a level of distrust between black Africans and the group's Arab leaders," the U.S.-based Center for Strategic and International Studies said in a report this month.
Peter Sharwood-Smith, Nigeria country manager at risk consultants Drum Cussac, stressed Boko Haram still appeared Nigeria-focused but perhaps was open to collaboration.
Aning said that while details and numbers remained sketchy, links between the groups had been growing for several years.
According to Sahara-researcher Jeremy Keenan, a "couple of dozen" Nigerians have trained with AQIM in the Sahara.
Citing African intelligence sources, CSIS went further, saying said there was evidence that some members of Boko Haram have trained with AQIM in Niger.
Weeks after the leaders of Niger and Nigeria met on security issues, Nigerian authorities said a Niger citizen had been arrested when a bomb-making factory was found near Abuja.
Clearly conscious of its Arab-dominated image, AQIM has broadcast videos seeking to show that it had succeeded in luring recruits from south of the Sahara, with one propaganda film last year showing fighters preaching in a number of languages, including Fulani, Haussa and Portuguese.
PUSH SOUTH AFTER FAILING IN NORTH
Al Qaeda's Sahara wing has raised its profile in the Sahel region in recent years after getting pushed south by Algeria's military into the vast and lawless desert regions of Mali, Niger and Mauritania.
While kidnappings and a slice of the trans-Saharan smuggling routes, now also ferrying cocaine, have swelled AQIM's coffers, the group has struggled to launch a spectacular attack in the zone. Vows of attacks in Europe have also failed to materialize.
Improved collaboration between the governments of Mali and Mauritania has led to attacks on AQIM training camps while, after the spate of kidnappings, potential targets are now few and far between.
"(Ties with Boko Haram) give them much more reach. Nigeria has much more juicy targets," the diplomat said of the oil-producing giant, compared to the sparse desert nations to the north.
AQIM's numbers are still relatively low -- in the hundreds, rather than thousands. Yet, analysts stress that the nature of their attacks means collaboration between even just a handful of people could lead to devastating results.
"Increased sophistication and operational tempo ... could depend in part on a few members who have received training and then return to construct explosives and possibly disseminate their knowledge," AQIM expert Andrew Lebovich wrote on the al-Wasat blog last month.
(Additional reporting by Tim Cocks in Lagos; Editing by Richard Valdmanis and Alison Williams)