At least 10 militants were killed on Wednesday as al-Shabaab positions were raided in southern Somalia by unknown forces, regional officials said
Al-Shabaab said it had been targeted overnight by "well-armed" troops who arrived in two helicopters for a ground battle in the town of Awdheegle.
The troops fired at al-Shabaab positions for 30 minutes, the group's spokesman Sheikh Abdiasis Abu Mus'ab told pro-insurgent radio Andalus.
He said the troops spoke English and appeared Western, adding that al-Shabaab "swiftly repelled" them and inflicted casualties on them.
"They could be Americans again hitting al-Shabaab bases" after US airstrikes allegedly killed 150 Islamists on Saturday, said a high-ranking regional security official who did not want to be named.
There was no confirmation for such allegations. Government officials in Mogadishu and the African Union military contingent in Somalia could not be reached for comment.
Adwheegle, located 55 kilometres south-west of the capital Mogadishu, has been under al-Shabaab control since African Union and Somali troops withdrew from the area last year.
At least five people were meanwhile killed in a car bombing in front of a police academy in Mogadishu.
The victims included three police officers and two civilians who were sitting in a nearby restaurant, senior police officer Ali Hirsi Ali Gab said.
The suspected would-be suicide car bomber, who was thought to have been catapulted out of the car by the explosion, was in a coma.
Al-Shabaab claimed the attack.
Elsewhere in Mogadishu, a bomb that was being transported on a motorcycle went off accidentally, injuring the driver who was arrested, police officer Mohamed Dahir said.
Two other people who were travelling on the same motorcycle escaped.