(CNN) The leader of the Islamic State of Iraq and Syria, Abu Bakr al-Baghdadi, seems to have broken his 11-month silence with a long audio message in which he mocks the United States, calls on jihadis to rally against the Syrian regime and insists that ISIS 'remains' despite its rapid loss of territory.

A spokesman for the US Office of the Director of National Intelligence, Timothy Barrett, told CNN that after analyzing the recording, the intelligence community has determined the message "appears to be authentic."

The speech seems to have been recorded relatively recently, as it references North Korean nuclear threats against Japan and the United States, as well as Syrian peace talks -- in which Russia, Turkey and Iran are trying to extend ceasefires across Syria.

The release appears to lay to rest claims by the Russian military that they had almost certainly killed Baghdadi in an airstrike near Raqqa on May 28. US officials say ISIS has largely been forced out of Raqqa as well as Mosul, and Baghdadi may be somewhere in the middle Euphrates River Valley.

That is an area that straddles Syria's border with Iraq, to which much of the group's leadership is thought to have relocated earlier this year.

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