One of the Isis' most hunted leaders delivered a rare speech that suggested the militants are feeling the pinch of recent territorial losses and the killing of key officials in US airstrikes.

Abu Mohammed al-Adnani, who is the chief spokesman for Isis (Islamic State) and a close aide to leader Abu Bakr al-Baghdadi, threatened Jews, pledged to defeat America and used typically defiant language to predict victory for the group's self-proclaimed caliphate.

But the defensive tone of the speech, delivered in an audio address posted on one of the Isis websites, suggested also that the militants are contemplating the prospect that their senior leadership will be wiped out and their last important cities be lost.

"Do you think you have won because you have killed one or more leaders? It is a false victory," he said.


"Even if we lose Raqqa or Sirte, we won't be defeated," he added, referring to Isis' self-proclaimed capital in Syria and the city in Libya it more recently conquered.

Just as significant was what the speech did not contain.

There was no claim of responsibility for the downing of the EgyptAir flight that crashed on Thursday into the Mediterranean. Investigators have yet determined what caused the plane to crash.

The speech also was not delivered by Baghdadi, despite feverish speculation throughout the day on social media by Isis supporters that the group's leader would be addressing them directly.

However, Adnani, like Baghdadi, has been rumoured to be dead on several previous occasions, and the address demonstrated that he is still alive. Baghdadi delivered his last speech in December and Adnani had not spoken publicly since October.

This address came after months of setbacks in which Isis has been pushed out of a string of key towns and cities, including Palmyra, Ramadi, Sinjar, and, most recently last week, the Iraqi town of Rutbah near the Syrian border. US officials also claim they are successfully targeting a growing number of the group's top leaders.

Adnani suggested that if Isis loses control entirely of its territory, it will resort to guerrilla warfare. Already, the group has been stepping up the pace of suicide bombings in Baghdad and elsewhere, in an apparent attempt to assert its presence even as it is defeated on the ground.

Brett McGurk, who is President Barack Obama's special envoy to the anti-Isis campaign, hailed the speech, tweeting that it was a sign that the US strategy was working. "Another sign of [Isis] leaders in deep hiding, afraid to appear in public or already dead," he tweeted. "Days are numbered."