Al-Shabab, which wants an Islamic state in Somalia, has been on the defensive in recent months
The US military has carried out air strikes in Somalia, reportedly targeting the leader of militant group al-Shabab.
It is not clear if Ahmed Abdi Godane was hit in the strikes some 240km (150 miles) south of the capital, Mogadishu.
One resident told the BBC he had seen the burnt-out remains of four vehicles. US officials say they will release further details later.
The al-Qaeda-linked group controls many areas of southern and central Somalia.
The US has carried out several air strikes in Somalia in recent years.
African leaders are meeting in Kenya on Tuesday to discuss the threat posed by al-Shabab and other Islamist militant groups such as Boko Haram in Nigeria.
Al-Shabab has not yet commented on the attack.
A US official quoted by the American media said “a senior al-Shabab operative” had been targeted but did not name him.
“We are assessing the results of the operation and will provide additional information as and when appropriate,” Pentagon spokesman John F Kirby said in a statement.
The governor of southern Somalia’s Lower Shabelle region said: “The Americans carried out a major air strike targeting a gathering by senior al-Shabab officials, including their leader Abu-Zubayr [a nom de guerre for Ahmed Abdi Godane].”
Residents of Hawai village, some 240km (150 miles) south of the capital, Mogadishu, say they heard three loud explosions and then saw thick black smoke rising.
One resident told the BBC he had seen the burnt-out remains of a car and three trucks but he was not able to see if there were any bodies inside.
The 22,000-strong African Union force says it has taken some towns from al-Shabab in recent days.
The 22,000-member AU force in Somalia is pushing al-Shabab into rural area in the south of Somalia
Civilians were able to return to the town of Bulomarer on Monday after al-Shabab militants were forced out by African Union and Somali soldiers
Al-Shabab militants on Sunday unsuccessfully tried to free other extremists held in a Mogadishu detention centre
The American action comes after al-Shabab rebels attacked a detention centre in Mogadishu on Sunday, in an apparent effort to free other militants detained there.
Somali officials said all of the attackers, as well as three government soldiers and two civilians, were killed.
The Pentagon and the US state department have supported the AU force that has driven al-Shabab from their former strongholds in the capital and some other urban centres since 2011.
The militants continue to carry out bombings and assassinations in Mogadishu.
Al-Shabab fighters want to overthrow the internationally supported Somali government and frequently attack government targets as well as neighbouring countries that provide troops to the AU force.
The group said it carried out last year’s attack on the Westgate mall in the Kenyan capital, Nairobi, in which at least 67 people were killed.