BEIRUT • The Islamic State in Iraq and Syria (ISIS) terrorist group appeared to be trying to keep morale high among its supporters in a new audio message which also called for attacks on the US during the holy month of Ramadan.

The audio recording reportedly featuring ISIS spokesman Abu Mohamed al-Adnani was posted online late on Saturday after much fanfare by ISIS supporters on Twitter.

"Will we be defeated if we lose Mosul, or Sirte, or Raqqa, or all the cities, and go back to how we were before?" Adnani asked. The three cities are ISIS strongholds in Iraq, Libya, and Syria respectively.

"No. Defeat is only losing the desire and the will to fight," he continued, in his first voiced speech since October.

He appeared to mock the United States, which is leading a coalition of countries in an air war against ISIS in Iraq and Syria, for failing to definitively defeat it.

He said even "20,000 air strikes" by the coalition had not destroyed ISIS.

He also called for attacks on the US and Europe during the holy month of Ramadan, which starts next month, an appeal he made at the same time last year when urging supporters to seek "martyrdom".

Last Friday, flyers apparently dropped by the coalition on Raqqa city in northern Syria urged residents to leave the city, perhaps ahead of an offensive by anti-ISIS forces to recapture it.

"It would appear ISIS is more clearly acknowledging its limitations in holding territory" while stressing the "idea of living on despite losses", wrote terrorism expert Aymenn al-Tamimi in reaction to Adnani's recording.

ISIS has seized swathes of territory in Syria and Iraq to create a self-styled "caliphate". Its leader, Abu Bakr al-Baghdadi, has received pledges of alliance from Islamist groups around the world.

AGENCE FRANCE-PRESSE