ISIS's number two man Abu Mohammad al-Adnani and the group's spokesman has been killed in Syria's Aleppo battlefields, according to the terrorist group's media sources.

“Abu Mohammad al-Adnani was killed in Aleppo battles,” Amaq news agency, which is an ISIS-affiliated news outlet, announced but did not comment on who was responsible for his killing or whether he died in an airstrike or in a ground attack.

“Al-Adnani in a video in 2014 affirmed his allegiance to Leader of the ISIL Abu Bakr al-Baghdadi. He was the first person who announced Nigerian Boku Haram’s allegiance to al-Baghdadi,” Amaq reported.

According to the source, he was appointed as ISIS's spokesman by al-Baghdadi last year.

The US Department of State had put a bounty as high as $5 million on Al-Adnani's head, which is the second highest amount for any ISIS official after the group's leader Abu Bakr al-Baghdadi.

Al-Adnani, who was known for his aggressive speaking style, sought to inspire lone wolf attackers in Western countries.

According to a statement from Amaq agency on Tuesday, al-Adnani died while inspecting military operations in the area of Aleppo, Syria.

This is while ISIS has not revealed his cause of death and announced that the group is determined to seek revenge for the killing.

"After a journey filled with sacrifice and fight against non-believers, the Syrian Gallant knight, Abu Mohammed al-Adnani, joined the convoy of martyr leaders," according to ISIS.