Bursts of gunfire followed the attack, which targeted the Italian Coffee cafeteria, located near the passport office. A Reuters photographer saw corpses sprawled on the ground at the scene of the blast.

Major Aden Ibrahim, a police official, told Reuters the attack was carried out by a suicide bomber.

Abdikadir Abdirahman, the director of AMIN ambulances, said his organization had removed eight bodies from the scene and taken more than two dozen wounded to hospital.

"The death toll may rise," he said.

Senior security officials were among the casualties, al Shabaab said.

"We are behind the blast," Sheikh Abdiasis Abu Musab, the group's military operations spokesman, told Reuters. "The targets were police, intelligence, military officials and immigration workers."

Musab said two generals were among the dead. Government officials were not immediately available and Reuters could not independently verify the claim.

In recent years, the Al Qaeda-linked group has lost large swathes of its territory to African Union peacekeepers supporting the U.N.-backed government.

But the insurgents frequently launch deadly gun, grenade and bomb attacks in Mogadishu and other regions controlled by the federal government. Many attacks are aimed at military bases but some also target civilians.

Earlier on Monday, three Somali soldiers on a ordnance-clearing mission were killed after a roadside bomb planted by the insurgents exploded 90 km (60 miles) north of the capital.

Somalia has been mired in conflict since 1991, when clan-based warlords overthrew dictator Siad Barre and then turned on each other.