The US Air Force is flying armed drones from a civilian airport in southern Ethiopia as part of a growing battle against Al-Qaeda linked Shabab militants in Somalia, the Washington Post reported Thursday.

The airfield in Arba Minch is part of a network of secret bases for unmanned aircraft in the Horn of Africa and the Arabian peninsula, the Post reported, citing unnamed US officials.

The US Air Force has spent millions of dollars to improve the airfield in Ethiopia to accommodate a fleet of Reaper drones that carry Hellfire missiles and precision-guided bombs, it said.

The US Air Force and the Pentagon declined to comment on the report.

Under President Barack Obama, the United States has increasingly turned to drones to carry out covert strikes against Al-Qaeda and allied militants in Pakistan, Yemen and Somalia.

The raids are conducted under the authority of the Central Intelligence Agency, not the military, but special operations forces and drone aircraft can be assigned to the spy agency for the strikes.

A spokesman for the 17th Air Force, which is assigned to operations in Africa, told the Post the drone flights "will continue as long as the government of Ethiopia welcomes our cooperation on these varied security programs."

The United States and Ethiopia both view Islamist militants in Somalia as a threat, and Washington backed Ethiopia's invasion of Somalia in 2006.

In support of the Ethiopian incursion, US AC-130 gunships carried out attacks from a base in Ethiopia. The government however ended the arrangement once it became public.

Kenya sent forces into southern Somalia 12 days ago to chase Shebab militants, but has denied the United States or other Western countries are actively involved in the military operations.