He was killed after US special forces raided a remote mountain cave complex hoping to capture him.

"Al-Sudani was responsible for fostering the growing presence of ISIS in Africa," Defence Secretary Lloyd Austin said.

He also allegedly funded the group's activities globally, Mr Austin added.

Analysts say that US troops were sent under orders of President Joe Biden to kill or capture Sudani, rather than using a less risky drone strike, which indicates his significance.

Details about the nature of the operation have not been released. However, the soldiers were drafted in via helicopter, according to the New York Times with Sudani killed after a gunfight broke out.

The operation comes after President Biden redeployed hundreds of US troops to the country after his predecessor, Donald Trump, pulled them out. However, those forces are reportedly only there to train Somali soldiers, rather than conduct operations.

In recent years, the Islamic State group has reportedly expanded its activities into several African countries, including Mozambique and the Democratic Republic of Congo.

However Islamic State is a relatively small group in Somalia, with the al-Qaeda linked group al-Shabab far more prominent - it controls many southern areas. 

Prior to joining Islamic State, Sudani allegedly did operational work for al-Shabab, assisting with training fighters. However he split from the group, along with others, to form an IS-affiliated group in the mid-2010s, according to security researcher Dino Mahtani.

He is accused of playing a "financial role with specialized skills which made him an important target for US counterterrorism action," an anonymous US official told the AFP news agency.

Sudani became "an important figure in the attempt by this faction of Islamic State to build a trans-national network straddling Central Africa and East Africa and now with links down to Mozambique," Mr Mahtani told the BBC's Focus on Africa radio programme.

His group are "master weapon-smugglers into the northern part of Somalia" and also have connections in DR Congo, Mr Mahtani continued, so was therefore a "high priority" to capture or kill.

The operation to target Sudani is said to have taken months to plan.