Kenyan forces have attacked the Somali port city of Kismayo, trying to drive militant group al-Shabab from its last major stronghold.

The Kenyan military says Friday's attack involved land, sea and air forces and was done in coordination with African Union and Somali government troops.

VOA's Somali Service reports Kenyan and Somali government troops control some northern neighborhoods of Kismayo but that most of the town, including the airport, is still in al-Shabab hands.

Two witnesses say the militants have mounted machine guns on the town's tallest buildings.

The Somali militia group Raskamboni is fighting on the side of the pro-government forces. The group's leader, Ahmed Madobe, told VOA that “we hope to take over the city within the coming hours.”

He noted, however, that al-Shabab relied economically on Kismayo and may fight to prolong its control.

Al-Shabab, which is formally allied with al-Qaida, has used Kismayo's seaport to raise money through taxes, as well as import weapons.

Kenyan forces entered Somalia last year after a series of cross-border kidnappings that Kenya blamed on the militant group.

Pro-Somali government forces have been moving toward Kismayo for more than a month, and Kenyan warplanes and warships attacked Kismayo earlier this week ahead of the attempt to push the militants out.

The United Nations refugee agency reported Friday that about 12,000 people left Kismayo in the past month, in some cases to avoid forced recruitment by al-Shabab.

The militant group is seeking to overthrow Somalia's government and impose a hardline form of Islamic law in the country. The group once controlled most of southern and central Somalia, but has lost most of its territory over the past 18 months to pro-government forces.