Islamist insurgents have seized the Somali port of Merka, located about 90 kilometers south of the capital, Mogadishu.
Residents say hundreds of armed al-Shabab militants took over the town without a fight Wednesday, after pro-government forces fled.
Merka is a key entry point for food and aid workers into Somalia. A spokesman for the U.N. World Food Program, Peter Smerdon, says the city appears calm and the WFP plans to continue using the port.
Islamist forces captured two other central Somali towns - Qoryoley and Bulo Marer - on Monday. The Islamists also control Kismayo, the other main port south of Mogadishu.
Al-Shabab is the military wing of the Union of Islamic Courts, an Islamic movement that ruled much of Somalia in the second half of 2006 and aims to impose sharia law in Somalia.
The United States considers the group a terrorist organization.
There has been no comment on the Merka takeover from Somalia's U.N. and Ethiopian-backed government.
The government has been unable to assert control over Somalia since its creation in 2004.
The country has not had a stable central authority since 1991 when a coup toppled President Mohamed Siad Barre.
Some information for this report was provided by AFP and Reuters.