Images posted on social media show a blood-spattered white vehicle, its windows shattered and the roof blown off by the blast in the region's administrative capital Garowe.

"The IED (improvised explosive device) attack occurred when the staff were travelling from their guest house to the office, normally a three-minute drive," UNICEF said in a statement.

Four more of its staff were seriously wounded, it added. Al Qaeda-linked al Shabaab has staged a string of attacks in Somalia and surrounding countries in its bid to impose its brand of Islam and overthrow a Somali government backed by Western donors and African peacekeepers.

"We are behind the Garowe attack," al Shabaab's military operations spokesman, Sheikh Abdiasis Abu Musab, told Reuters. Mohamed Abdi, a police officer at the scene of the attack, earlier said Kenyans and Somalis had been killed, but UNICEF said its staff hailed from a range of countries.

Nicholas Kay, the U.N. Special Representative for Somalia, said on his Twitter feed he was "shocked and appalled by loss of life". Al Shabaab, which once ruled much of Somalia, has been driven out of major strongholds in military offensives launched last year by the Somali army and African Union peacekeepers. Puntland, on the northeastern tip of Somalia, had in the past largely avoided the regular attacks seen in other areas.

However, attacks by the militant group have intensified this year. Earlier this month, al Shabaab fighters killed 148 people in a university campus in the Kenyan town of Garissa, about 200 km(120 miles) from the Somali border. The group has said it wants to punish Kenya for sending troops to Somalia as part of the AU force.

--reuters--