US forces have "likely killed" a top al-Qaeda suspect during a US military raid in Somalia, a US official has told the BBC.
The suspect, Saleh Ali Saleh Nabhan, is wanted over 2002 attacks on a hotel and an Israeli airliner in the Kenyan port of Mombassa.
He has been on the FBI's list of top suspects for years.
The claim followed earlier reports that foreign troops had attacked Islamist militants in southern Somalia.
A second US official said US special forces carried out the attack early on Monday Washington time.
The official said the operation had been "successful" and he believed Nabhan was dead.
The earlier reports said the troops wore uniforms with French insignia, and had attacked a vehicle carrying Islamists from the al-Shabab group.
A French military spokesman denied his country's forces were involved.
The reason for the confusion over the identity of the troops was not immediately clear.
Witnesses said the soldiers took away two men, and two bodies were left in the road after the attack in the southern coastal town of Barawe.
Somali sources have told the BBC that six helicopters were involved in the attack on two vehicles.
Reuters news agency cited a US official as saying special forces had flown by helicopter from a US navy ship and fired on a vehicle that they believed was carrying Nabhan.
He added that the body believed to be Nabhan's had been taken into custody.
Spanish news agency Efe and Reuters also reported witnesses and al-Shabab sources as saying the Kenyan-born Nabhan had been killed.
Al-Shabab are said to have links to al-Qaeda, and to have been reinforced with foreign fighters.
Nabhan is suspected of bombing of an Israeli-owned hotel in Kenya and a failed attempt to shoot down an Israeli airliner in 2002.
The authorities in Kenya also regard him as a suspect in two attacks on US embassies in the region in 1998.
The US, which like France has troops stationed in neighbouring Djibouti, has carried out air strikes against Somali Islamist groups it accused of links to al-Qaeda in recent years.
Monday's assault comes several weeks after a French security adviser held by militants in Mogadishu managed to get free. A colleague seized at the same time remains in captivity.
Somalia has not had a functioning central government since 1991.
Rival Islamist factions are battling forces loyal to the weak UN-backed government, which controls only small parts of the capital Mogadishu.