MOGADISHU, Somalia — Kenyan troops invaded al-Shabab’s last stronghold in Somalia Friday, coming ashore in a predawn beach landing at Kismayo that appeared likely to deprive the Islamist insurgents of their last big money-making enterprise.

African Union troops from Kenya, Uganda and Burundi have combined over the last 18 months to kick al-Shabab out of the capital of Mogadishu and take a series of smaller towns that the insurgents fled to.

By Friday afternoon Kenyan defense forces said their ground troops were also steadily approaching Kismayo from the west. Al-Shabab, which is allied with al-Qaida, had earned money by collecting taxes on goods arriving at the Indian Ocean port, so the loss of the stronghold would be a double blow to the armed fundamentalist group that began attacks in 2007 and ultimately controlled all but a few blocks of the capital.

The assault is likely to send al-Shabab fighters underground. Hardcore fighters may unleash suicide bombs and ambushes, but less dedicated fighters could melt back into their communities, further reducing al-Shabab’s strength.

The African Union force said some al-Shabab fighters already have contacted military officials in recent days, saying they wanted to defect.

The assault rocks al-Shabab onto its heels and comes as the government finally is getting organized, having moved in recent weeks from a U.N.-backed transitional government to one in which parliament, which itself was recently elected by elders, chose a new president. Last month, Somali leaders endorsed a new provisional constitution that expands rights for Somalis.

Speaking on the sidelines of the U.N. General Assembly in New York, Kenya’s Deputy Prime Minister Musalia Mudavadi called the entry of Kenyan forces into the Somali port “a significant victory.”

Residents in Kismayo contacted by The Associated Press said Kenyan troops had taken control of the port but not the whole city.