Mogadishu -  A US military drone strike on a vehicle carrying explosives in Somalia has removed "an imminent threat to the people of Mogadishu" by the al-Shabaab extremist group, the US Africa Command said on Tuesday.

The airstrike was carried out early on Tuesday morning about 65km southwest of Somalia's capital, the US statement said, adding that no civilians were killed. It was not immediately clear how many al-Shabaab fighters may have been killed.

A senior Somali intelligence official said the airstrike largely destroyed a minibus travelling near the rebel-held village of Mubarak in Lower Shabelle region. The official spoke on condition of anonymity because he was not authorised to speak to the media.

The al-Qaeda-linked al-Shabaab has been blamed for the massive truck bombing in Mogadishu in October that killed 512 people, wounded more than 300 others and left more than 60 missing. Only a few attacks since the ones on September 11, 2001 have killed as many people, according to the Global Terrorism Database at the University of Maryland.

Al-Shabaab, the deadliest Islamic extremist group in Africa, often targets high-profile areas of Mogadishu including hotels, military checkpoints and the presidential palace.

The US military has carried out 32 airstrikes this year against the Somalia-based al-Shabaab and a small but growing presence of fighters linked to the Islamic State group. The Trump administration early this year approved expanded military operations against extremists in the Horn of Africa nation, as the Trump administration puts counterterrorism at the top of its foreign policy agenda for Africa.

More than 500 US military personnel are now in Somalia, the US Africa Command said last month.