Earlier, Daesh* confirmed the death of the group's longtime leader Abu Bakr al-Baghdadi and reportedly named Abu Ibrahim al-Hashimi al-Quraishi as his successor.
The move came just days after the Trump administration claimed the Daesh* leader blew himself up during a raid by US special forces in Syria's Idlib province.
The hunting down of Daesh* leader Abu-Bakr al Baghdadi and his apparent suicide with an explosive vest has generated skepticism and uncertainty among both US military leaders and experts.
Damascus in fact even expressed doubts about the Trump administration's story.
Syrian President Bashar Assad said Thursday that Damascus had no contacts with the United States on the elimination of al-Baghdadi and will not believe that he was really killed until reliable evidence is presented.
"We had no contacts with American authorities on the elimination of al-Baghdadi. More importantly, we do not know whether this operation actually took place or not", Assad said in an interview with Syrian state run television channels.
However, US Central Command Commander Gen. Kenneth McKenzie during a press briefing on Wednesday said that defence intelligence analysts confirmed al-Baghdadi's identity by comparing his remains to an old file sample taken from the time he spent in Camp Bucca in Iraq in 2004.
Al-Baghdadi's remains were then buried at sea in an undisclosed location after his identity was confirmed within 24 hours of his death, McKenzie continued.
However, the US government now expects Daesh* to attempt to carry out a retribution attack against US forces, McKenzie added during the same briefing.
Retired US Army Colonel Doug Macgregor, a historian, combat commander, and tactician said he believed al-Baghdadi's death would not stem the threat of international Islamist terror.
"Killing one terrorist has at most symbolic significance", Macgregor said.
Macgregor also supported the refusal of US forces to release any more video of the raid as it might leak valuable intelligence that could compromise future missions.
It was "probably" reasonable to keep the rest of the footage classified to prevent other terrorists from studying it, he said.
Former CIA case officer Phil Giraldi, a member of Veteran Intelligence Professionals for Sanity said that al-Baghdadi's death saved the US government from the security challenges, nationalist criticism and other complexities of keeping him under lock and key for decades.
The raid footage does again suggest that the US government prefers to kill terrorists rather than having to send them to Guantanamo and hold them for 20 years without trial as in the case of Khaled Sheikh Mohammed, he added.
Giraldi also noted that, as was the case when 9/11 mastermind Osama bin Laden was hunted down and killed eight years ago, the US refusal to provide more details of how the body was disposed of was bound to generate new conspiracy theories and suspicions.
Terrorism expert Professor Rohan Gunaratna, head of the International Centre for Political Violence and Terrorism Research (ICPVTR) at Nanyang Technological University in Singapore agreed the United States was following common practice in refusing to release many details about the operation.
"No government, including the United States, will release all the footage of a counterterrorist operation. I think that it is very important for governments to not make public the entire documentation, including footage, of such sensitive operations", Gunaratna said.
Sources and methods used in such operations needed to be concealed for a very long time because otherwise, the terrorists would benefit, Gunaratna explained.
Gunaratna also stressed that the United States had a deep responsibility to eliminate the very group that emerged in Iraq and extended into Syria and beyond to other countries.
"Because the genesis of the Islamic State is in Iraq, and if not for the United States intervention in Iraq in 2003, the group that has been known as ISIS [IS] and is now known as Islamic State would have never emerged", he emphasised.
US Special Forces called the attack that led to al-Baghdadi's death Operation Kayla after the young Christian missionary in her 20s from the US state of Arizona who was repeatedly personally raped by al-Baghdadi before he beheaded her, according to Yazidi eyewitnesses who escaped captivity.
*Daesh (also known as ISIS/ISIL/IS) is a terrorist group outlawed in Russia