By Ahmed Mohamed

BAIDOA, Somalia, April 3 (Reuters) - Somalia's Islamist insurgents killed three soldiers on Thursday near the government's Baidoa stronghold, the latest hit-and-run assault in a rebellion spreading from its Mogadishu epicentre.

Members of the al Shabaab militant group, the latest addition to the United States terrorist list, struck in Qansah Dheere, 60 km (37 miles) southwest of the interim government's base in Baidoa.

"Early this morning, a heavily armed al Shabaab group ambushed us, killing three of my soldiers, wounding two others and blowing up one of our cars," Bay region Governor Abdifitah Mohamed Ibrahim told Reuters by phone.

"The fighting stopped after nearly an hour. We do not know the enemies' losses."

Baidoa is in south-central Somalia and remains one of the government's strongest bases with plenty of Ethiopian military presence to protect it.

Al Shabaab spokesman Mukhtar Abu Mansur declined to comment.

Security experts say al Shabaab is leading the insurgency against President Abdullahi Yusuf's interim government, which defeated the militant group and its allies in the Somalia Islamic Courts Council with Ethiopian military help last year.

The bulk of the fighting takes place in the anarchic coastal capital Mogadishu, where the insurgents are waging a campaign of Iraq-style assassinations, roadside bombings and artillery attacks against the government and its Ethiopian allies.

At least 6,500 people have died in Mogadishu since the government took over the city in December 2006, thousands more were wounded and more than 600,000 have fled cycles of attacks and reprisals that have pulverised a city already in ruins.

Since early December, al Shabaab fighters or local militiamen claiming allegiance to the group have carried out assaults on government troops in far-flung outposts and held the towns briefly.

With Somalia's shifting allegiances, it is often difficult to tell whether it is part of a concerted campaign or clan or money disputes al Shabaab has taken credit for, diplomats say.

Al Shabaab was the feared military wing of the court coalition that controlled most of southern Somalia in the second half of 2006, imposing strict Islamic law and threatening Yusuf's plans to impose his government's authority.

With several members trained in Afghanistan and what the United States says are connections to al Qaeda, Washington in late February put it on its list of terrorist groups.

The United States has long feared the vacuum of authority in Somalia -- without an effective central government since 1991 -- is a prime territory for al Qeada to plan and carry out attacks into the rest of eastern Africa. (For full Reuters Africa coverage and to have your say on the top issues, visit: http://africa.reuters.com/ ) (Additional reporting by Aweys Yusuf in Mogadishu, Writing by Bryson Hull; Editing by Janet Lawrence)

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