NAIROBI, Kenya — Somali commandos backed by U.S. forces raided two al-Shabab checkpoints at which the extremists extort money from commercial vehicles, killing several fighters, Somali intelligence officials said Wednesday.

The officials also said two U.S. airstrikes in the area during the overnight raid destroyed an explosives-laden minibus that was prepared for a complex attack on an unspecified location. The officials spoke on condition of anonymity because they were not authorized to speak to the media.

The U.S. Africa Command in a statement said four extremists were killed in a “self-defense airstrike” after U.S. and partner forces came under attack. It said no civilians were involved.

Residents of Awdhegle, a farming village in Lower Shabelle region in southern Somalia, told The Associated Press they had heard gunfire and explosions.

"Something big happened here last night. We only know that al-Shabab was under attack, said one elder, who gave his name only as Yusuf for fear of reprisal from the al-Qaida-linked extremists.

"Then we woke up to find fighters sealed off the whole area in the morning," he said.

The U.S. military has stepped up the fight against al-Shabab since President Donald Trump took office, carrying out more airstrikes in 2017 than over the previous decade. The U.S. has carried out at least 38 airstrikes this year.

Al-Shabab "uses portions of southern and central Somalia to plot and direct terror attacks, steal humanitarian aid, extort the local populace to fund its operations and shelter radical terrorists," the U.S. statement said.

The extremist group uses widespread extortion of businessmen and travelers to fund its high-profile attacks in major cities such as Mogadishu, collecting millions of dollars a year.

The U.S. military in coordination with Somali forces, as well as an African Union force, have targeted al-Shabab's finance operations in recent weeks.

Last month, Somali intelligence officials said at least four missiles hit a base for over 30 extremists assigned to collect livestock taxes from nomadic communities in the central Mudug region.

In October, the AU force said the head of tax collection in Lower Shabelle region was killed after an ambush on a meeting of al-Shabab fighters in southern Somalia.