US air strikes in Somalia are aimed at al-Qaeda leaders in the region, and based on "credible intelligence", a Pentagon spokesman has said.
The US used AC-130 gunship in raids over Somalia
In its first official comment on the air strikes, the Pentagon said a raid was carried out on Sunday but declined to say if it had hit its target.
The US has long said al-Qaeda suspects linked to the 1998 US embassy bombings in East Africa took refuge in Somalia.
At least 19 people were killed in US air raids, local Somali elders say.
Fresh air raids were reported near the town of Afmadow on Monday and Tuesday, but it is not clear if these were carried out by the US, or by Ethiopian forces which back the transitional Somali government.
The air strikes are taking place days after the Union of Islamic Courts, which had taken control of much of central and southern Somalia during the past six months, was routed by soldiers from Ethiopia and Somalia's government.
Latest reports from Mogadishu say unknown assailants have fired rocket propelled grenades at a building housing Ethiopian troops and Somali government forces.
Two explosions were heard, followed by a brief but heavy exchange of automatic gunfire.
'No safe haven'
The US air strikes were carried out by an Air Force AC-130, a heavily armed gunship that has detection equipment and can work under the cover of darkness.
White House spokesman Tony Snow said the US action was a reminder that there was no safe haven for Islamic militants.
"This administration continues to go after al-Qaeda," he said.
"We are interested in going after those who have perpetrated acts of violence against Americans, including bombings of embassies in Kenya and Tanzania."
Somalia's interim President, Abdullahi Yusuf Ahmed, said the US had the right to bomb those who had attacked its embassies.
But Italy - the former colonial power in central and southern Somalia - condemned the US strikes.
Italian Foreign minister Massimo d'Alema said Rome opposed "unilateral initiatives that could spark new tensions".
UN Secretary General Ban Ki-moon expressed "concern" that the air strikes could lead to an escalation of hostilities.