The US military has been flying armed drones over both countries from a base in Djibouti and is planning to build a second base in Ethiopia, a report by the Washington Post says.
The report added that the drones on missions over Somalia and Yemen take off or land at the base an average of 16 times per day.
The Lemonnier base has also become home to a squadron of US F-15 fighter jets, which it reports are flying combat missions over Yemen.
The US is also known to operate drones from two other East African countries — Ethiopia and the Seychelles islands.
The base in the Seychelles that was previously used to fly surveillance drones will now host armed drones capable of flying their lethal payloads the more than 1,500 kms that separate the Indian Ocean island chain from Somalia and the African mainland and back.
However, drone operations from Ethiopia and Seychelles are nothing compared to the one at Camp Lemonnier. According to the report Lemonnier is the centerpiece of an expanding US network of drone and surveillance bases in Africa.
Washington has also been carrying out assassination attacks using the unmanned aircraft in other countries including Afghanistan, Libya and Pakistan.
The United States claims the CIA-run strikes are aimed at militants. But witness reports and figures offered by local authorities indicate the attacks have led to massive civilian deaths.