Witnesses in central Somalia say fighting between rival Islamist groups has killed at least 25 people.

Clashes broke out in the town of Guriel early Sunday between hardline al-Shabab militants and fighters of another Islamist group, Ahlu Sunna Wal-jam'ah.

Residents say the fighting had stopped by mid-day and that Ahlu Sunna was in control of the town.

Most of those killed were combatants.  At least 20 other people were wounded in the fighting.

Al-Shabab is the most prominent of the insurgent groups that have battled the Somali government and allied Ethiopian troops for the past two years.  

The insurgent groups have clashed at times as they jockey for position ahead of the expected Ethiopian withdrawal.

Ethiopia's decision to remove its remaining 3,000 troops has raised concern the fragile Somali government may not survive.

The insurgents now control much of southern and central Somalia, with the government holding only the capital, Mogadishu, and the parliament seat of Baidoa.

An internal power struggle forced President Abdullahi Yusuf to resign last month.  Interim President Sheikh Aden Madobe told Reuters news agency Saturday that al-Shabab poses the biggest threat to Somalia.

Al-Shabab, which the United States considers a terrorist group, has moved to enforce a strict form of sharia (Islamic) law in the areas it controls.

Some information for this report was provided by AFP and Reuters.