Signs of impending battle, however, have become frequent. On Saturday, Kismayo was rocked with artillery from the sea. Three civilians died and four more were wounded, according to residents. Meanwhile, al Shabab has levied new taxes, food prices are skyrocketing and thousands have fled the city in anticipation of the attack, swelling the population of camps for the displaced as far away as Mogadishu.

"The port is not functioning. The people are using whatever food they have saved, and there is no direct way to Kenya and the outside region except for very rough routes," said Abdirashid Bure Omar, a local elder in Kismayo, who blamed both al Shabab and the Kenyan forces for restricting road routes. Omar was interviewed by phone – al Shabab doesn’t allow independent journalists in areas under its control – and it wasn’t possible to verify his statements.

Col. Ali Adam Hamud, the spokesman for African Union troops – who are in Somalia to defend the country’s internationally recognized government – said he was aware of the bombardment of Kismayo but that he didn’t know whether African Union countries were involved. Kenya, Uganda and Burundi all contribute troops to the African Union presence.

The United .States denied persistent speculation that its warships had fired on Kismayo. Ambassador James Swan, the Obama administration’s special representative for Somalia, said U.S. forces weren’t involved in the efforts to uproot al Shabab. "What we are seeing in the region is an African response to an African crisis," he said.

But Swan also said the U.S. was encouraging those efforts, and the United States has contributed heavily to stabilization efforts in Somalia, including $355 million in direct support to countries who are part of the African Union military force. The U.S. views al Shabab as its most dangerous adversary in East Africa.

Even if al Shabab is dislodged from Kismayo, the group is unlikely to disappear. United Nations reports detail how the group has expanded its reach underground into fundraising and recruiting cells across East Africa.

McClatchy special correspondent Mohammed Yusuf contributed to this article from Nairobi.