Isis says second-in-command, Abu Muhammed al-Adnani, has been killed in Syria

No details yet on how he died, but Aleppo province has seen fierce fighting

Terror group says Adnani was ‘martyred while surveying the operations to repel the military campaigns against Aleppo’

The terror caliphate Isis has announced that its chief spokesman and one of its most senior figureheads has been killed in Syria.

Abu Muhammed al-Adnani was “martyred while surveying the operations to repel the military campaigns against Aleppo [province],” the group’s Amaq News Agency said on Tuesday without providing any details. No date of his death was given although a eulogy of Adnani was released, dated 29 August 2016.

Adnani was believed to be the second most important leader of Isis, after Abu Bakr al-Baghdadi, in charge of all of its operations beyond the bounds of its self-declared caliphate in Syria and Iraq. He is also one of the group's longest-serving top commanders. Some western offiicals believe he met al-Baghadi in a US prison camp after being arrested in Iraq in 2005.

The Amaq agency vowed to take revenge against the “filthy cowards in the sect of disbelief.” It said a generation raised in Isis-held territory will strike back.

If the death of Adnani is confirmed, it could represent the most significant kill ever of a top lieutenant of Isis by its enemies. Far more than just a spokesman for the group, he was a top strategist, particularly when it came to orchestrating terror attacks overseas, including in western European countries like France. It was Adnani, western officials believe, who helped plan some of those attacks and deployed Isis soldiers from the caliphate to carry them out.

He also stood out for his chilling choices of words when calling for a new unleashing of terror in the West. In one statement to the Isis faithful, Adnani urged the killing of the "filfthy French", adding that if it proved difficult to achieve that with either a bullet or a knife, the next best thing was to "crush them with your car". That staement seeemd to take on fresh significance after the terror attack in Nice in July when a 19-tonne cargo lorry was driven through a crowd killing 86 people.

While US officials said they were aware of the report, they could not immediately add any details or indeed confirm the death of Adnani.

Isis has come under increasing military pressure both from the US and its allies as well as from Russia and the forces of the Syrian government. While it holds territory in Aleppo governorate it is not in control of Aleppo city, where rebels are fighting fiercely with Syrian government forces.

Last year the US government put up a $5 million reward for information that would lead to Adnani’s capture.

The military outlook for Isis in Syria has become more precarous in recent weeks as US-backed Syrian Democratic Forces, an alliance of Kurdish and Arab militias, and Syrian rebels backed by Turkey have advanced into its terriotory in northern Syria effectively cutting off its access to Turkey and strangling its route out of that country for bringing in new recruits.

A Syrian born in the city of Idlib, Adnani reportedly swore allegiance to the jihadist movement a decade ago. Earlier this year, the Iraqi government said he had been wounded in an aerial attack in the western province of Anbar and had then repaired to Mosul in northern Iraq.

Adnani frequently appeared as the face of Isis in its proclamations and threats to its foreign enemies, as when it urged its followers worldwide to launch attacks against the US and its allies during the Islamic holy month of Ramadan this year.