Somali commandos backed by US forces raided two al-Shabaab checkpoints at which the extremists extort money from commercial vehicles, killing several fighters, Somali intelligence officials said on Wednesday.The officials also said two US 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 authorised to speak to the media.The US Africa Command had no immediate comment.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-Shabaab was under attack, said one elder, who gave his name only as Yusuf for fear of reprisal from the al-Qaeda-linked extremists."Then we woke up to find fighters sealed off the whole area in the morning," he said.The US military has stepped up the fight against al-Shabaab since President Donald Trump took office, carrying out more airstrikes in 2017 than over the previous decade. The US has carried out at least 37 airstrikes this year.Al-Shabaab 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 US military in coordination with Somali forces, as well as an African Union force, have targeted al-Shabaab'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-Shabaab fighters in southern Somalia.* Sign up to News24's top Africa news in your inbox: SUBSCRIBE TO THE HELLO AFRICA NEWSLETTERFOLLOW News24 Africa on Twitter and Facebook.