Al Qaeda-linked al Shabaab militants have abandoned the southern Somali port city of Kismayu, their last bastion in the country, a day after an assault by African Union troops.

Al-Shabab rebels pulled out of a key port city in southern Somalia, the group said Saturday, a day after Kenyan troops invaded and marched toward the city center and seaside port that long served as the militants' key source of funding, officials said.

Residents in Kismayo said they woke to find police and government headquarters abandoned by the militants, sparking a looting spree of the government and police headquarters.

"They withdrew from here last night. The town is not under anyone's control now," Mohamed Hassan, a resident, said. "People feel some relief now. We hope no more fighting will take place."

FRANCE24's correspondent in Nairobi, Duncan Wood, said that Kenyan forces are situated largely to the north of the city and moving slowly. "They may encounter roadside bombs and also there is a small chance that this withdrawal is effectively propaganda and that the Kenyan army may just be lured into a trap."

The withdrawal came about 24 hours after Kenyan forces made a beach landing and as inland troops from Somalia and Kenya moved toward the port city from the west.

"Looting and chaos is going on here. Thugs are taking advantage of the vacuum," Maryan Hussein, another resident, said. "The abandoned houses are being ransacked and the streets are occupied by people carrying belongings."

Col. Cyrus Oguna, a spokesman for the Kenyan military, said five al-Shabab fighters were killed in a battle overnight. Two commanders were killed in the fighting, the military said.

He said the Kenyan forces are still verifying the reports that al-Shabab had pulled out of Kismayo. "For now we are treating it as a theory," he said.

The Kenyan troops landed by boats in the northern part of Kismayo on Friday and moved toward the port, he said. He said that al-Shabab lost "many, many militants, including some key commanders" during battles on Friday that involved helicopter gunships.

Al-Shabab used Twitter to announce the news it was leaving Kismayo.

"Last night, after more than 5 years the Islamic administration in Kismayo closed its office," the tweet said. "Kismayo shall be transformed from a peaceful city governed by Islamic Shari'ah into a battle-zone between Muslims" and invaders.

Al-Shabab found little popular support in Kismayo because of the conservative brand of Islam it tried to impose on residents. Al-Shabab carried out public executions, whippings and amputations as punishments, and enforced a conservative dress code.

Al-Shabab was forced out of Mogadishu in August 2011 and lost one of its major sources of funding when it could no longer tax businesses in the city's main market. Since then the taxes al-Shabab charged on goods coming into Kismayo's port were seen as its last major funding source.

As it no longer holds any major cities in Somalia, al-Shabab is expected to operate more as an insurgent force that carries out suicide and roadside bomb attacks.

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