"They killed Abu Bakr al-Baghdadi because they feared the ISIL leader's capture could end up in the disclosure of secrets related to the terrorist group," Hakem al-Zameli was quoted as saying by the Arabic-language service of Russia Today on Monday.
He, meantime, warned of emergence of a new leader for the ISIL.
Al-Zameli said the US has used a worn-out method once again to eliminate a dead tree, adding that the same method was used in 2010 against Abu Musab al-Zarqawi, the al-Qaeda ringleader in Iraq, when the Iraqi forces were about to capture him.
Baghdadi died "whimpering and crying" in a raid by US special forces in northwest Syria, President Donald Trump claimed on Sunday.
Baghdadi killed himself during the raid by detonating a suicide vest after fleeing into a dead-end tunnel, Trump said in a televised address from the White House.
He was positively identified by DNA tests 15 minutes after he died, he said. "He was a sick and depraved man and now he's gone."
The Russian military on Sunday questioned the official US account of the military raid that killed al-Baghdadi, saying it was not aware of any US military operations in the region.
In a statement, Russian Defense Ministry Spokesman Major General Igor Konashenkov said the Russian military “does not have reliable information” on a US Special Operations raid in Syria’s Idlib province, adding, “The increasing number of direct participants and countries that allegedly took part in this ‘operation,’ each one giving completely contradictory details, raises legitimate questions and doubts about its existence and especially the level of its success.”
In a statement that followed the raid, Trump thanked Russia for its assistance, as well as Turkey, Syria, Iraq and the Syrian Kurds.
Russia maintains a major base in Syria at Lattakia. Konashenkov said, however, that the Russian military had observed no strikes by US aircraft in the region.
“Firstly, on Saturday and in recent days no air strikes were made on the Idlib de-escalation zone by US aircraft or the so-called ‘international coalition’ were recorded,” Konashenkov said. “Secondly, we are not aware of any alleged assistance to the passage of American aviation into the airspace of the Idlib de-escalation zone during this operation.”
Konashenkov argued in his statement that Syrian government backed by Russian air power had defeated ISIL, saying that al-Baghdadi’s death “has absolutely no operational significance on the situation in Syria or on the actions of the remaining terrorists in Idlib”.