Q+A: Somali-Yemeni militant ties in the spotlight

(Reuters) - The rise of al Qaeda's Yemen-based branch as a security worry after its claim of a failed December 25 bid to blow up a U.S. airliner has stirred concern about its ties to like-minded militants in nearby Somalia.

Here are questions and answers about links between al Qaeda in the Arabian Peninsula (AQAP) and Somalia's al Shabaab, an al Qaeda-inspired insurgency in the failed Horn of Africa state.

WHY WORRY NOW?

On January 1, an al Shabaab official, Sheikh Mukhtar Robow Abuu Mansuur, said the group was ready to send reinforcements to AQAP should the United States attack its bases in Yemen.

The United States is stepping up security cooperation with Yemen following the December 25 incident, involving a Nigerian who is reported to have said the plot was hatched in Yemen.

Robow caused concern because al Shabaab is an effective force that has seized large areas of south and central Somalia.

Its successes, like those of AQAP, have helped to inspire a small but enthusiastic global community of al Qaeda supporters.

Getting to Yemen is unlikely to be difficult.

While an international anti-piracy flotilla patrols the Gulf of Aden, hundreds of dhows carrying contraband shuttle between the two countries undetected every week, and Somalia's pirates continue to roam the seas and seize vessels for ransom.

Regional concerns increased on January 2 when Somali defense minister Sheikh Yusuf Mohammad Siad accused AQAP of sending two boat loads of weaponry to al Shabaab fighters in the rebel-held southern port of Kismayu in recent days.

While Yemen has for years been an important source of arms for Somalia, the trade is normally operated by well-established arms brokers and shippers, not by militants themselves.

SO IS THE LINK-UP RHETORICAL, OR REAL?

For propaganda purposes the groups have tended to proclaim more of a relationship than really exists in practice.

But the December 25 incident shows AQAP has ambitions beyond its immediate region. And while there are tensions over cultural and language differences between Arabs and Somalis in al Shabaab, to date the demands of the insurgency have overridden these.

AQAP military commander Qasim al-Raymi has fought in Somalia and has written on the need to back Somalia's revolt. He was one of a 23-strong group of al Qaeda militants who escaped from prison in Yemen in 2006 and went on to form AQAP. Some others in that founding group had also fought in Somalia.

Security experts say Yemenis make up a sizeable part of a foreign contingent that fights with al Shabaab's Somali rank and file and supplies bomb-making and communications expertise.

By one estimate there are about 500 or more foreigners in Shabaab's ranks, which experts say may number 5,000 or more.

WHO ELSE IS SHUTTLING BETWEEN YEMEN AND SOMALIA?

Militants do not figure heavily in the traffic across the Gulf of Aden. For now, that remains dominated by organized crime -- arms traders and people and drug smugglers backed by powerful local and regional vested interests.

There is also illicit trade in fuel, cement and food to remote natural ports in Somalia via routes that are adjusted rapidly to respond to new markets or government countermeasures.

Regional experts say there have been sporadic reports of Somali fighters in Yemen. But they speculate that some of these may be Saudi Arabia-bound illegal immigrants press-ganged by Yemeni groups into fighting on their side.

Some observers say it is unlikely AQAP would take up Robow's offer in any substantial way, unless it was truly desperate.

AQAP has other resources, they argue. Its close links to al Qaeda's Arab-dominated leadership in south Asia suggests it would be able to obtain more recruits and financing than other al Qaeda affiliates could expect in similar circumstances.

IS ROBOW'S OFFER SINCERE?

At least three interpretations of Robow's offer are circulating among Somalia watchers.

One is that it genuinely reflects the intention of al Shabaab to send fighters, if AQAP is hit by the United States.

A second is that it is mere bluster: Shabaab's overwhelming priority is to hold the ground it has gained and if possible gain more. It cannot afford to lose any fighters right now.

A third is that this is a unilateral attempt by Robow, seen by many as one of the more nationalist of al Shabaab's top men, to ingratiate himself with hard-line colleagues in the leadership after he was sidelined in a falling out over policy.

According to one proponent of this third view, there have been strains inside al Shabaab over its core aims: Some in the movement wish to pursue a largely domestic agenda to grab power and transform the country into an Islamic state.

Robow has been identified with this view, which experts say is shared by the rank and file. He is using the Yemen issue in a tactical bid to shore up his position, experts say.

In opposition to the nationalist trend are voices calling for al Shabaab to participate fully in al Qaeda's global quest by extending the movement's reach beyond Somalia's borders. This line is heavily promoted by al Shabaab's foreign brigade.

(Reporting by William Maclean, Editing by Giles Elgood)