Advances by the al Qaeda affiliate, which included briefly capturing villages within 50 km (30 miles) of Mogadishu last month, have left residents of the capital on edge amid rumours al Shabaab could target the city.

The army has recaptured those villages, but al Shabaab has continued to advance in the countryside, leading the government to deploy police officers and prison guards to support the military, soldiers have told Reuters.

The town attacked on Wednesday, Adan Yabaal, lies around 245 kilometres north of Mogadishu and has been used as an operating base for raids on al Shabaab.

President Hassan Sheikh Mohamud, who hails from the area, visited Adan Yabaal last month to meet with military commanders there about reinforcing them.

After early morning prayers, we heard a deafening explosion, then gunfire," Fatuma Nur, a mother of four, told Reuters by telephone from Adan Yabaal. "Al Shabaab attacked us from two directions. I am indoors and fighting is still going on."

The outcome of the battle was not immediately clear, with government forces and al Shabaab giving conflicting accounts.

Captain Hussein Olow, a military officer in Adan Yabaal, told Reuters that government troops had pushed back the militants.

Al Shabaab, which has waged an insurgency since 2007 to seize power and rule based on its strict interpretation of Islamic Sharia law, said in a statement that its forces had overrun 10 military installations and captured the town.

National government officials did not immediately respond to requests for comment.

The fighting comes as the future of international security support to Somalia has grown increasingly precarious.

A new African Union peacekeeping mission replaced a larger force at the start of the year, but its funding is uncertain, with the United States opposed to a plan to transition to a U.N. financing model.