Instead of directly attacking Somalia's Shebab militants, the United States provides crucial intelligence and training to other armies battling the Islamists in a deliberately low-profile approach, officials said Tuesday.

A bloody four-day siege of a Nairobi shopping mall claimed by Shebab has focused attention on US-backed efforts to weaken the insurgents, which American officials claim have been effective despite the attack over the weekend.

From airfields stretching from Djibouti to Entebbe, the US military and intelligence agencies fly surveillance drones to track Shebab's movements while American special operations forces have taught tactics to troops from Kenya, Ethiopia and the Somali government, officials and experts say.

"It is definitely a light footprint approach," Seth Jones, a former adviser to special operations commanders in Afghanistan and the Pentagon, told AFP.

"The US presence has been minimal, overtly anyway," said Jones, an author of books on insurgencies and terrorism.

The intelligence handed over to regional allies, rather than a modest amount of military hardware, represents the most important part of the assistance, he said.

"The US does collect a lot of information and passes it along."

Defense officials believe "indirect" methods have proved a success, and that the Nairobi attack was partly an attempt by the group to grab headlines and retaliate for battlefield defeats in Somalia.

"Not long ago, the government of Somalia controlled only a few blocks in Mogadishu and now they have control over a large area in southern Somalia," said a US military officer, who spoke on condition of anonymity.

The Shebab is definitely "under pressure" but "they're clearly not gone," the officer said.

President Barack Obama's administration has no plans to dramatically change its policy and move towards drone strikes or raids by special forces, officials said.

Since Al-Qaeda's bombing of US embassies in Kenya and Tanzania in 1998 and the attacks of September 11, 2001, the US military began building up a logistical network across East Africa, arranging access to airfields and ports with a base in Djibouti serving as the main hub.

About 3,000 troops are deployed at Camp Lemonnier in Djibouti, which oversees training by special forces and other military assistance in the region.

Another 150 US military personnel are currently in Kenya, including trainers, while a similar number are posted in Ethiopia, defense officials said.

The Pentagon spends hundreds of millions of dollars in support of the African Union mission in Somalia offering logistical help, equipment, training and troop transport.

After 9/11, the US military created a joint task force in East Africa with a "capture or kill" mission. But drone strikes and special forces' raids gradually gave way to advising and assisting Somalia's neighbors.

Unlike Pakistan or Yemen, drone strikes targeting Al-Qaeda linked militants in Somalia have been the rare exception.

Washington has preferred to work behind the scenes partly because a big footprint would produce a backlash and invite comparisons to the troubled US deployment in Somalia in the 1990s.

"The US role in Somalia is definitely problematic. The US has a history in Somalia, some of it's good, some of it's not so good," Jones said.

The attack in Nairobi, which killed 61 civilians, coupled with Shebab's recruitment of Americans of Somali heritage, prompted calls from some US lawmakers for the United States to go after the militants with American firepower.

But the Obama administration will be reluctant to change its strategy unless there is a clear sign that Shebab poses an imminent threat to US embassies in the region or that its American recruits are heading back to the United States to stage attacks, experts said.

The fact that some of the attackers were US nationals raises the "level of concern" for Washington, "in part because there's always a concern that they will come back to the United States and stage attacks here," said Kim Cragin, who has written about terror threats and religious extremism.

There has been a debate "over whether Shebab has been in its last gasp or whether it can rebound from the setbacks," said Cragin, a senior political scientist at the RAND Corporation think tank.

The Nairobi assault indicates the group cannot be counted out just yet, she said.

With access to airfields in Kenya, Uganda, South Sudan and Ethiopia, ports in Kenya, and other forces based in Sigonella, Italy, the US administration has a network at the ready if it chooses to fight.