The US military on Tuesday announced its deadliest airstrike against the al-Shabaab extremist group in Somalia in nearly a year, killing about 60 fighters.The US Africa Command said Friday's airstrike occurred near the community of Harardere in Mudug province in the central part of the country. According to its assessment no civilians were injured or killed, the statement said.It was the largest US airstrike since one on November 21, 2017, killed about 100 al-Shabaab fighters. The statement gave no further details about what was targeted in this latest strike and the US Africa Command did not immediately respond to questions.The US military has carried out more than two dozen airstrikes, including drone strikes, this year against the al-Qaeda-linked al-Shabaab, the deadliest Islamic extremist group in sub-Saharan Africa.Somalia on Sunday marked the first anniversary of al-Shabaab's deadliest attack, a truck bombing in Mogadishu that killed well over 500 people. It was one of the world's deadliest attacks since 9/11 and the worst extremist attack ever in Africa.The United States, which also has targeted a small number of fighters linked to the Islamic State group in northern Somalia, has increased its military presence in the long-chaotic Horn of Africa nation since early 2017 to about 500 personnel after President Donald Trump approved expanded military operations.Al-Shabaab, which seeks to establish an Islamic state in Somalia, continues to hold parts of the country's south and central regions after being chased out of Mogadishu several years ago. The group, estimated at several thousands of fighters, still carries out deadly attacks against high-profile targets such as hotels and checkpoints in the capital and other cities. It also remains a threat in parts of neighbouring Kenya.While some observers have questioned the effectiveness of airstrikes by the US and Kenya and raised concerns about civilians being killed, the US military maintains that they "reduce al-Shabaab's ability to plot future attacks, disrupt its leadership networks and degrade its freedom of maneuver within the region."Somali forces in the next few years are expected to take over responsibility for the country's security from an African Union peacekeeping force, which already has started withdrawing hundreds of personnel.The US says it continues to support that transfer even as some US military officials have joined AU officials and others in expressing concern that Somalia's forces are not yet ready.* Sign up to News24's top Africa news in your inbox: SUBSCRIBE TO THE HELLO AFRICA NEWSLETTERFOLLOW News24 Africa on Twitter and Facebook.