Amaq News, the information agency connected to the Islamic State (IS), has issued a statement but declined to say the cause of his demise.
But the Russian government claimed that the terrorist leader died in the middle of a Russia-initiated airstrike in Aleppo.
Al-Adnani's death marked the highest-profile killing yet of an ISIS member.
Although Abu Bakr Al-Baghdadi is the inspirational and strategic leader of the terrorist organization, it is Al-Adnani who stands as the public figure for the group.
Understandably, his popularity has convinced a lot of observers that he will eventually assume total leadership should anything happens to the self-proclaimed Caliph Ibrahim.
Earlier in January, Al-Adnani was allegedly injured during a coalition airstrike. The senior lieutenant is regarded as more than just a mouthpiece considering that he is well-known for ordering operatives to attack countries that are affiliated with the US-led coalition.
His presence in the group has made him more dangerous since he is believed to be in-charge of the external operations which carried out the attacks in Paris.
Born Taha Subhi Falaha in 1977 in Syria's province of Idlib, Al-Adnani has been with ISIS from the very beginning.
Back in 2014, he is the first to declare a caliphate in parts of Syria and Iraq. He has also said that Western supporters of the IS have the religious duty to launch lone-wolf attacks.
In Washington, Peter Cook, the Pentagon's spokesman, has confirmed that an American "precision strike" near Al-Bab in Syria had targeted Al-Adnani on Tuesday night although his death remains uncertain.
With the IS reeling from numerous counterattacks over the past few months, the 39-year old Syrian's death is a blow to the organization's operational strategy.
In the Northern part of the province where the IS spokesperson has been supposedly killed, the ISIS is facing difficult scenarios which include air strikes from Turkey, Russia and the US plus ground attacks from Syrian rebels and Kurdish forces.
