NAIROBI, Kenya -- African Union and Somali soldiers captured another key town from Somalia’s al Qaida affiliate Monday, seizing the fishing port of Merca and boxing in the Islamist rebels even further in a steady military campaign aimed at capturing their last major stronghold, the port of Kismayo.

Al Shabab rebels, who once ruled much of Somalia under Taliban-style shariah law, had held Merca, a coastal town of white buildings and exotic Indian Ocean beaches about 45 miles south of Mogadishu, Somalia’s capital. Al Shabab merged earlier this year with al Qaida, but a variety of forces, including troops from Kenya and Ethiopia who invaded last year, have pushed it back.

Accounts from the town said al Shabab officials and fighters had fled south toward Kismayo three hours before the African Union troops arrived. Tensions were high in Merca now, residents said.

“We are worried about our security,” one resident, Nur Mohamed, said in a phone interview. “Everybody is staying inside his house. No one is moving outside. Businesses are closed.”

Officials of the Somali government in Mogadishu gloated over the news, proclaiming that al Shabab’s rule will soon be finished.

“Our troops are controlling the town. We captured it peacefully," said Abdukadir Mohamed Nur, the regional governor appointed by the federal government. "We have already planned our offensives. We have a good strategy, and our troops, backed by the AMISOM forces, will assure the control of Lower Shabelle region."

His statement referred to the African Union Mission in Somalia, the regional force composed mainly of Ugandan, Burundian and Kenyan troops.

No comments were available from al Shabab.

Troops from AMISOM, the Somali government and Kenya, whose forces invaded Somalia last year, have beaten back Al Shabab steadily over the past year . The capture of Merca now raises the likelihood that the Islamist rebels in Kismayo, 210 miles away, will face assault from multiple fronts, with seasoned Ugandan and Burundian forces attacking from the north and Kenyan troops attacking from the west.

Kenya had promised to capture Kismayo by the end of August, but the offensive has been delayed a number of times, most recently by negotiations with Ethiopia over who’ll rule the region afterward.