The US military official said "dozens" of US advisers participated in the overall operation, adding that while the al Qaeda affiliate al-Shabaab was known to have influence in the area, the local village was seen as friendly to the federal government.
The U.S. special operations forces were fighting alongside about 800 troops from the Somali National Security Forces and Kenyan Defence Forces when they were attacked late on Friday by mortars and small arms fire.
Al-Shabab militants launched a deadly attack on US and Somali forces Friday, hitting them with explosives and heavy gunfire.
The attack marks the first known combat death of a USA service member in African since the October 4 ambush of United States and Nigerian forces which killed four U.S. troops and five Nigerians.
Though U.S. -backed operations and airstrikes have dented al-Shabab, the militants have continued to carry out deadly attacks in Somalia, including a bombing in October of past year that left some 300 people dead in the capital of Mogadishu.
The Islamic militant group, al-Shabab, claimed responsibility for the attack friday that killed one US service member and wounded four others.
About 500 US troops are deployed in Somalia.
President Donald Trump called the soldiers heroes Friday night.
The US had pulled out of the Horn of Africa nation after 1993, when two helicopters were shot down in Mogadishu and bodies of Americans were dragged through the streets. The group was blamed for a truck bombing in Mogadishu in October that killed more than 500 people and raised concerns about its ability to build larger explosives.
"The mission's objectives were to clear al-Shabaab from contested areas, liberate villages from al-Shabaab control, and establish a permanent combat outpost created to increase the span of Federal Government of Somalia (FGS) security and governance", said the Africom statement.
Late a year ago USA drone strikes also began targeting a small presence of fighters linked to the Islamic State group in Somalia's north.
The US have been providing advice, assistance and aerial surveillance during the mission.
The names of victims will not be released until the families have been notified.
Hundreds of newly trained al-Shabab fighters perform military exercises in the Lafofe area south of Mogadishu, Somalia, on February 17, 2011.
The US's role in AFRICOM's area of responsibility has come under heavy scrutiny following an October ambush in Niger that left four soldiers dead.