The US government says it believes it knows the real name of Abu Sayyaf, the key ISIS commander it says was killed during a US raid in Syria over the weekend.

"While he had a number of aliases, we believe his real name to have been Fathi Ben Awn Ben Jildi Murad al-Tunisi," a US official said Tuesday on condition of anonymity.

Al-Tunisi, until now known by the nom de guerre Abu Sayyaf, was killed in a heavy firefight after he resisted capture in a US special operations forces raid in eastern Syria, the US Defense Department has said.