MOGADISHU, Somalia – Kenyan troops invaded al-Shabab’s last stronghold in Somalia on 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 Mogadishu and take a series of smaller towns that the insurgents fled to. By Friday afternoon, Kenyan Defense Forces said that its 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.