The mayor of Somalia's war-torn capital, Mohamed "Dheere" Omar, told the BBC Somali Service during a Monday interview that the mass exodus of civilians from Mogadishu is due to the al Shabaab fighters.

"Al Shabaab is calling civilians on private numbers and threatening to kill them," Mayor Dheere said.

He said the Somali transitional federal government appeals to civilians "to show calm" in the face of growing calamity.

Mogadishu Mayor Mohamed Dheere

"A strong security initiative begins today. We hope to clean it [Mogadishu] up within one week," the mayor said confidently.

He did not elaborate, but stated clearly that a "new offensive" against the al Shabaab insurgency has began in the Somali capital.

Since the weekend, an estimated 2,000 extra Ethiopian troops entered Mogadishu from neighboring regions to reinforce troops there after insurgent attacks escalated.

More than 15 mortars pounded two Ethiopian military bases inside Mogadishu last night, but casualty figures were difficult to ascertain due to military secrecy.

"Al Shabaab is making the troubles. They are launching mortars on government positions," Mayor Dheere said, promising that the government is fully confident that it can secure Mogadishu.

"We are 100% sure we will secure Mogadishu. The real Mogadishu is peaceful. The troubled area is areas west of Industry Road," the mayor said, referring to a part of Mogadishu built after the collapse of the central government in 1991.

He said areas west of Industry Road are "disorganized and lack proper roads," making it difficult for security forces to operate.

The mayor of Mogadishu said the government was working closely with aid agencies, especially the UN's World Food Program, to help feed fleeing civilians. More than 88,000 people fled Mogadishu over the past weekend, the UN's refugee agency estimated.

He skidded around a question regarding public complaints about the Mogadishu police force, especially forces loyal to the mayor's office.

"I don't have a special police," Mayor Dheere said. "I am a governor and the government police take orders from me."

Al Shabaab is the youth core of the Islamic Courts militia ousted from Mogadishu by the Ethiopian army in January. The U.S. and Ethiopian governments accuse the group's leaders of having links to international terror networks.

But the al Shabaab guerrillas say they are fighting for the liberation of Somalia from the grip of Ethiopia's armed forces.