The Islamic State group has accused Somalia's Al Qaeda affiliate of killing several jihadi leaders who defected to its side, including a Sudanese sentenced to death for killing a U.S. diplomat in Khartoum and his driver.

A detailed report posted on two ISIS-affiliated websites on Friday said al-Shabab leaders ordered the killing and detention of dozens of jihadis who expressed their willingness to join ISIS. They include Mohamed Makawi, a Sudanese who took part in the drive-by shooting of John Ganville and his driver in Khartoum on Jan. 1, 2008.

Makawi and another accomplice, Abdelbasit Haj Hamad, were among four sentenced to death in Sudan for killing Granville but escaped from prison in 2010.

The U.S. offered up to $10 million for information leading to the capture of the two men.