US troops accompanied Somali forces in a helicopter raid against Shebab insurgents in Somalia, a Pentagon spokesman said Wednesday.
US aircraft were used in the operation against the Al-Qaeda-affiliated group, which the spokesman described as an "advise, assist and accompany mission" with the Somali army.
"We did go on the mission but we did not go all the way to the objective," Navy Captain Jeff Davis said.
The raid overnight Tuesday to Wednesday came just days after US warplanes and drones killed an estimated 130 Shebab fighters training for a major operation, according to the Pentagon.
Special forces operatives in two helicopters targeted the Shebab-controlled town of Awdhegele, about 50 kilometers (30 miles) west of Somalia's capital Mogadishu, Somali government officials and a Shebab spokesman said.
"We have reports Shebab militants suffered casualties," local district commissioner Mohamed Aweys told reporters.
It was not immediately clear what the objective was, but helicopter raids in the past have been hostage rescue missions, such as a US commando operation in 2012 to free two aid workers who had been held for three months by the group.
Davis said there are a small number of US troops in Somalia supporting an African Union mission and the Somali national army "specifically in their fight against al-Shebab."
The number of militants killed by US strikes in Somalia has increased in recent years from 4 in 2011 to 41 in 2015, according to data compiled by the think-tank the New America Foundation.
The latest raids came after Shebab stepped up its attacks since the start of the year.
In January, the group attacked a camp of Kenyan peacekeepers in the south of the country that was part of the African Union mission.
The attack killed more than 100 soldiers, security sources in Nairobi said.
In late February, Shabab killed more than 40 people in a series of attacks in Mogadishu and Baidoa in southwestern Somalia.
The insurgents have also bombed the presidential palace in the capital and managed to place a bomb in a plane leaving Mogadishu for Djibouti last month.
The device exploded shortly after takeoff, ripping a hole in plane's side but killing only the suspected bomber before the aircraft landed safely.
The attack showed the group was able to evade the heavy security at Mogadishu's airport.
Observers say the group aims to disrupt Somalia's first presidential election in 40 years, planned for later this year.