Six people were killed and the mayor of Mogadishu wounded in a bombing at the mayoral offices in the Somali capital, the government said on Wednesday, in an attack claimed by Al-Shabaab militants.

United Nations special envoy James Swan had met the mayor, Abdirahman Omar Osman, and left just before the blast at the headquarters of the Banadir district, which encompasses Mogadishu, according to the mission's Twitter account.

"Six people, including two district commissioners and three directors, were killed in the terrorist attack this afternoon," Information Minister Mohamed Abdi Hayir Mareye told reporters.

As well as the mayor, five others, including district commissioners, were injured in the blast and being treated by doctors.

The Al-Qaeda linked Al-Shabaab militant group claimed responsibility for the "well-prepared operation", saying they were targeting Swan.

UN sources said Swan left the premises about an hour before the attack.

A security source, who asked not to be named, said a suicide bomber had entered a hall where the officials were meeting and detonated the blast inside.

"The mayor was wounded in the blast and he is currently being treated. Some of the commissioners of Mogadishu district have also been wounded," deputy mayor Mohamed Abdullahi Tulah told the government's radio station Muqdisho.

Security forces are investigating the incident.

"The blast occurred inside but we are not sure what exactly caused it, some reports we are getting indicate it was caused by a suicide bomber... and there are casualties," said security official Mahdi Abdirahman.

"The blast was very heavy, and I saw people fleeing, some with shrapnel wounds, outside the Banadir administration headquarters," said witness Mohamud Shariif, referring to the regional government offices.

In a statement, Al-Shabaab said they had "killed many of the enemy".

Mogadishu is regularly hit by attacks by the Al-Shabaab, which has fought for more than a decade to topple the Somali government.

The city was on Monday struck by a car bomb that left 17 dead and more than two dozen wounded.

SOURCE: SAUDIGAZETTE