KISMAYU, Somalia (Reuters) - Two U.S. missiles hit a house in southern Somalia on Monday, according to local officials, in a strike Washington said was directed at "known terrorists".

It was the fourth U.S. air strike in 14 months on Somalia, where Washington believes local Islamist insurgents are giving shelter to wanted al Qaeda figures.

"We launched a deliberate strike against a suspected bed-down of known terrorists," a senior U.S. official, who declined to be named, told Reuters in Washington.

Residents of Dobley, a remote Somali town 220 km (140 miles) from the southern port city of Kismayu on the Kenyan border, believed the missiles were targeting senior Islamist leaders meeting nearby.

Dobley district commissioner Ali Hussein Nur said six people were killed, but a local politician who had visited the scene and who asked not to be named, said only three people were wounded.

The U.S. official said it was too early to know what damage had been inflicted, or whether any people were injured or killed. The official declined to give details on the type of weapon used.

The Somali politician said Sheikh Hassan Turki, a local militant cleric, and other leaders from a militant Islamist group from Mogadishu were meeting in the vicinity. The Islamists have been waging a bloody insurgency against Somali government forces.

ASSESSING DAMAGE

"The town is very tense. People have started fleeing because they fear there might be more attacks," he said.

A man in Kismayu, who said the house belonged to him, told Reuters his daughter had been wounded and four of his cows killed in the attack.

"We do not know whether the missiles were fired by the American AC-130 plane which is still flying over the city. All we know is they dropped from the sky," Mohamed Nurie Salad told Reuters in Kismayu.

He said he was returning to Dobley to assess the damage, which he had been told about over the telephone.

On January 8, 2007, a U.S. AC-130 gunship struck Islamists in southern Somalia in Washington's first overt military action there since pulling out of a U.N.-backed peacekeeping mission in 1994 after the "Black Hawk Down" incident.

That attack, and another with the same kind of airplane shortly thereafter, struck Islamists fleeing from Ethiopian and Somali troops who cornered them in southern Somalia during a two-week war to rout the militant movement.

On June 21, a U.S. Navy ship fired missiles at Islamist fighters and foreign jihadists hiding in the mountains in the northern Puntland region.

The United States accuses Somali Islamist insurgents of harbouring al Qaeda fugitives responsible for planning and executing the 1998 U.S. embassy bombings in Kenya and Tanzania.

It provided intelligence and some military support to Ethiopia's intervention to help the Somali interim government in late 2006.

The Horn of Africa country has had no central government since a dictator was overthrown in 1991. An interim government formed in 2004 is struggling to assert its authority and is battling the Islamists in the capital Mogadishu.