Islamic militants have shot dead two Britons of Somali origin and two Kenyans, as they took control of the violent central Somali town of Baladwayne, officials and residents said today.

The fighters were from the notorious al-Shaabab milita, closely linked with the Islamic extremists who have captured several towns across Somalia recently and appear to be making a comeback more than a year after Ethiopian troops invaded on Christmas Eve 2006 in an attempt to push them out.

Abdi Aden Adow, the local police chief, identified the Britons as a 32-year-old woman and the principal, a 70-year-old man, whose sons live in Birmingham, England. Local residents said the man had returned to Somalia after years of living abroad to build the Hakab Private English School, where the murdered took place last night.

The four were said to have been shot in the head, execution-style, as al-Shaabab gunmen took control of Baladwayne. They torched the home of the local administrator and freed several prisoners as they swept through town. Police forces had fled before the attack occurred.

"Al-Shaabab fighters entered the town and suddenly attacked houses of government officials," Ahmed Elmi, a resident, told the Reuters news agency. "Then they attacked a school where they killed two Kenyans, a British woman and a Somali man with a British passport."

Britain does not have an embassy in Somalia. "Our High Commission in Nairobi is urgently investigating these reports but we can't confirm anything at this stage," said the Foreign and Commonwealth Office in London.

The killings were the latest in a spate of attacks in Somalia, which has descended even deeper into anarchy in recent years. The country has not had a functioning government since the dictator Mohamed Siad Barre was ousted in 1991. Baladwayne is the capital of Somalia's Hiran province, which has seen some of the worst attacks recently.

Early this month, Murray Watson, a Briton, was kidnapped with a Kenyan colleague in the south of the country. A UN Refugee Agency car was fired upon in the once-peaceful region of Puntland last week, and the aid agency Doctors Without Borders withdrew all its staff after three of its workers were killed in a roadside bomb in February.

Also in February, the US Government branded Al-Shaabab a foreign terrorist rganisation. The group welcomed the move, which it said would help attract new recruits.

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