In another major setback for international efforts to bring peace to Somalia, a violent power struggle between two sub-clans in the port city of Kismayo is fueling fear that an all-out clan war could erupt at any time and destabilize a key region of southern Somalia.  VOA Correspondent Alisha Ryu reports from our East Africa Bureau in Nairobi.

After days of skirmishes between Marehan and Majerteen sub-clan militias in the country's third-largest city, residents of Kismayo say heavy fighting erupted on Friday, killing and wounding dozens of people.

The Marehan and the Majerteen belong to the larger Darod clan, recognized as one of the four major clans in Somalia. 

A Somali aid worker in Kismayo, Ali Bashi, tells VOA that the militiamen of both sub-clans are technically Somali government troops and government supporters, who are nevertheless bitterly divided along clan lines.

Bashi says Friday's clash in Kismayo between the Marehan and the Majerteen follows a battle the two sides fought on April 23. 

After the battle, Majerteen soldiers withdrew from Kismayo to the town of Bulo Gadud, 35 kilometers away, leaving the city and its strategic port in the hands of the Marehan.

In recent days, Majerteen troops have been seen moving closer to Kismayo.  On Thursday, at least four people were wounded when one group of clan militiamen attacked another. 

The Marehan's grip on Kismayo appears now to have tightened.  VOA has learned that Marehan troops entered Bulo Gadud on Friday and declared victory over the Majerteen sub-clan.

Somali interim President Abdullahi Yusuf

But the latest fighting has many Somalis concerned that interim President Abdullahi Yusuf, who is a Majerteen and kinsman to the soldiers defeated by the Marehan, could launch a retaliatory strike against the Marehan and start a major clan war. 

Since capturing the Somali capital, Mogadishu, from Islamist forces in late December, President Yusuf's Ethiopian and western-backed government has promised to end clan politics and unify the country after 16 years of civil war.

Ethiopian soldiers guard massive cache of weapons at a military compound in Mogadishu, Somalia, 14 June 2007

Meanwhile, a government-imposed nighttime curfew in Mogadishu went into effect on Friday. The government says the curfew is necessary to curb attacks by insurgents who have targeted government officials, Somali police, and Ethiopian troops.

In recent weeks, Ethiopian and Somali troops have searched businesses and houses throughout the capital, confiscating several truckloads of munitions and weapons, including land mines, mortars, rockets, and missiles.