Abu Mohammed al-Adnani, Islamic State spokesman and its leader in Syria, has been killed in Aleppo province, according to ISIS’ own news agency Amaq. Pentagon told Reuters that it had carried out an air strike against a "senior IS official" but did not confirm that it was behind al-Adnani's death.

One of the longest-serving Islamic State (IS, formerly ISIS / ISIL) figureheads, al-Adnani was reportedly killed “while surveying the operations to repel the military campaigns against Aleppo.” The Syrian province in the midst of a multiple-way battle between the Syrian government, assorted militants and Islamic State.

BREAKING: #ISIS 'Amaq reported that ISIS spokesman Abu Muhammad al-'Adnani was killed in #Aleppopic.twitter.com/br7YslGPPL — SITE Intel Group (@siteintelgroup) August 30, 2016

Despite a lengthy tribute, dated August 29, Amaq made no mention of who was responsible for killing al-Adnani, or whether he was killed from the air or from the ground.

The US confirmed that it targeted the town of al-Bab, outside the city of Aleppo, in a recent air strike, and a rebel source told Reuters that this was also the last known whereabouts of al-Adnani. Washington said it was still reviewing the results of its operation, and was not prepared to issue a public statement.

There were earlier reports that al-Adnani had been injured in an air strike in Iraq in January this year.

Al-Adnani, a Syrian citizen in his late 30s, had a $5 million US Department of State bounty on his head – the second biggest for any IS official after the movement’s leader Abu Bakr al-Baghdadi.

2)When calling for lone wolf attacks in West, #ISIS fighters/supporters quote #Adnani more than any other individual pic.twitter.com/3N91HL8VSe — Rita Katz (@Rita_Katz) August 30, 2016

Known for his aggressive, florid speaking style, al-Adnani sought to inspire recruits and lone wolf attackers in the West, and his calls to arms were often cited by ISIS adepts. Western media also reported that he was the head of a special intelligence unit, responsible for planning complex terrorist attacks in Europe.

Adnani was powerful orator, spoke a poetic Arabic, arguably more influential than Baghdadi himself, possibly why he voiced most audio notes — Eisa Ali (@EisaAli_RT) August 30, 2016

According to SITE Intel Group, which specializes in the inner workings of jihadi organizations, ISIS threatened revenge for the death, at the hands of a new generation of Islamists who have been born in the current conflict zone, who “love death more than life.”

But for all the public fury, the death is likely to be a major blow to the retreating Islamic State, which also lost its top military commander Abu Omar al-Shishani – known as Omar the Chechen – earlier this summer.

Aleppo, once Syria’s biggest city, remains a key battleground, as well as being home to nearly 300,000 civilians, who remain trapped in the midst of a humanitarian crisis.

For the Syrian government, which is fighting alongside units from the Hezbollah movement, it is a chance to drive out the rebels, who are receiving military assistance, supplies and safe passage from Turkey. Meanwhile, Islamic State has its forces outside the city, and is keen to stop an offensive towards its Syrian stronghold of Raqqa.

The once-powerful group has suffered a sequence of turnarounds in recent months, pressured from Kurds on one side, and the Iraqi army on another. It was recently estimated by the US that it is down to about 15,000 fighters, while its income has more than halved.