Somalia: Failed State
What drives al-Shabab?
Lighting up Somalia
US special forces have carried out a raid on a senior leader of the al-Shabab Islamist group in Somalia, US officials say.
The unnamed officials said a US Navy Seals team had targeted the man after approaching a villa in the southern town of Barawe by sea.
There are conflicting reports about whether the raid was successful.
It was said to have been prompted by last month's deadly attack on the Westgate shopping centre in Kenya.
In a separate development, US officials say that an al-Qaeda leader accused of the 1998 bombings of the US embassies in Kenya and Tanzania has been captured by US forces in Libya.
Nazih Abdul-Hamed al-Ruqai - better known as Anas al-Libi - was said to have been seized by US forces near Tripoli.
The New York Times and NBC both reported that the al-Shabab leader had been captured in Somalia, but the Times then said he was believed to have been killed in a pre-dawn firefight - and that the US troops were forced to withdraw before that could be confirmed.
However, the Associated Press news agency quoted unnamed sources as saying that the Seals failed to find the intended target.
"The Barawe raid was planned a week and a half ago," a US security official told the New York Times.
"It was prompted by the Westgate attack," added the official, who was speaking on the condition of anonymity.
Al-Shabab earlier told the BBC that "white soldiers" had arrived by boat in Barawe and rebels had repulsed them, losing a fighter.
Local group commander Mohamed Abu Suleiman said the raid had failed and the group remained in control of Barawe.
Separately, Reuters carried a statement by Sheikh Abdiasis Abu Musab, al-Shabab's military operations spokesman, which said that British and Turkish special forces were involved.
He said the commander of the British force was killed, and four SAS and a Turkish soldier were wounded.
Commando raids on al-Shabab
5 October 2013: Helicopter and boat strike by unknown forces on Barawe
12 January 2013: Two French commandos killed in failed mission to rescue agent held in Bulo Marer
14 September 2009: US Navy commandos kill Kenyan-born al-Qaeda commander Saleh Ali Saleh Nabhan in raid on Barawe
French soldier dies in Somali raid
Fury at 'al-Qaeda killing'
Both Britain and Turkey said their forces had not been involved in the operation.
Barawe residents said say they were woken up by heavy fighting before dawn.
"Gunfire broke out for about 10-15 minutes," an eyewitness told AFP news agency.
Al-Shabab has said it carried out the attack in the Westgate shopping centre in Kenya's capital Nairobi which left at 67 people dead. Many more people were injured after militants stormed the centre on 21 September.
Western navies tasked with fighting piracy patrol the seas off Somalia, which has been beset by conflict for more than two decades.
In 2009, US Navy commandos attacked and killed an al-Qaeda leader, Kenyan-born Saleh Ali Saleh Nabhan, in a daylight raid on Barawe.
Washington has also used drones in Somalia to support the government and African Union forces in their battle against al-Shabab.
France carried out an unsuccessful raid to free a French intelligence agent in January. Two French commandos were killed and al-Shabab later reported that it had killed the agent.