The United States launched an airstrike on an al Shabaab site in Somalia on Saturday, which it claimed was used by the group to carry out an attack on an African Union military base in Bulo Marer on Friday.

US Africa Command said in a statement that the air raid "destroyed weapons and equipment unlawfully taken by al Shabaab fighters."

Media outlets pointed out that US AFRICOM failed to specify when, where, or what are the stolen weapons targeted, raising speculations over the nature of the operation.

"US Africa Command conducted an airstrike against militants in the vicinity" of Bulo Marer on Friday, in support of the Federal Government of Somalia and the AU force known as African Union Transition Mission ATMIS, the statement read.

Read more: Al Shabaab attacks AU base in Somalia

The military command added that according to its "initial assessment", no civilians were injured or killed. 

Ugandan troops were stationed in the Bulo Marer base when it was raided on Friday by the Al-Qaeda-affiliated group.

In a statement on Friday, ATMIS said, "At around 5 a.m. today, ATMIS Forward Operating Base (FOB) in Buulo Mareer, approximately 120 km [75 miles] southwest of Mogadishu in Lower Shabelle region was attacked by al Shabaab militants using Vehicle Borne Improvised Explosive Devices (VBIEDs) and suicide bombers."

The soldiers were able to destroy the militants' weapons and force them to retreat with reinforcements from the ATMIS aviation unit and allies, the statement continued.

Al Shabaab has been waging an insurgency against the central government for more than a decade. It managed to be active in parts of Somalia and other countries of the Horn of Africa. Despite claiming readiness to negotiate earlier this year, the group continued to carry out attacks in different regions of the country.

The 20,000-strong ATMIS force - consisting of personnel from Uganda, Burundi, Ethiopia, Kenya, and Djibouti - has amped up military operations against the terrorist organization over recent years.

Al Shabaab militants were driven out of the capital in 2011 by an African Union force, but the group still controls swathes of the countryside. It continues to launch deadly strikes on civilian and military targets, with popular hotels and restaurants frequently hit.

Last August, Somalian government forces and affiliated groups, in addition to ATMIS, launched a comprehensive offensive against al Shabaab.

The AU mission is planned to hand over its responsibilities to Somalia's security and armed forces by 2024.