WASHINGTON - A US forces in Somalia called in an air strike on Thursday that killed five fighters from the al Qaeda-linked militant group al Shabaab, the Pentagon said.

The US forces had been advising Ugandan soldiers with the African Union mission (AMISOM) during an operation against an illegal taxation checkpoint when the Ugandans got into a firefight with 15-20 al Shabaab fighters.

Pentagon spokesman Captain Jeff Davis said no American forces were wounded on the ground during the incident, which took place west of Mogadishu, the capital.

"US forces were not involved with this firefight. We were nearby but not directly involved ourselves," Davis told a Pentagon news briefing, adding that the American forces were further back from the fighting, acting in an advisory role.

The United States has about 50 military personnel inside Somalia and has repeatedly targeted the group in recent months, including a strike on a senior al Shabaab leader in April and another on a training camp in March that killed some 150 fighters.

Al Shabaab was pushed out of Mogadishu by African Union peacekeeping forces in 2011 but has remained a potent antagonist in Somalia, launching frequent attacks in its bid to overthrow the Western-backed government.

The group, whose name means "The Youth," seeks to impose its strict version of ‘sharia’ in Somalia, where it frequently unleashes attacks targeting security and government targets, as well as hotels and restaurants in the capital.

Al Shabaab was also behind deadly attacks in Kenya and Uganda, which both contribute troops to an African Union peacekeeping force in Somalia.