Moscow's claim that Russian air strikes in Syria had killed prominent Daesh leader Abu Muhammad al-Adnani is false, U.S. defense officials told Reuters on Wednesday.

"Russia's claim is a joke," one of the U.S. defense officials said, speaking on condition of anonymity.

The Pentagon on Tuesday said it had targeted Adnani, who Daesh has said was killed in Aleppo province.Amaq reported that Adnani was killed "while surveying the operations to repel military campaigns against Aleppo".Adnani is a Syrian from Idlib who pledged allegiance to Daesh's predecessor al-Qaeda more than a decade ago and was once imprisoned by U.S. forces in Iraq, according to the Brookings Institution.The Syrian was known for his fiery calls for attacks on Arab and Western targets.

Earlier this year, he called for massive attacks during the Muslim holy month of Ramadan. He has also called for attacks in Western countries, telling Muslims in France on occasion to attack "the filthy French" in any way they could, including "crush them with your car."