The Islamic State group (IS) has released an audio message purportedly from its leader, Abu Bakr al-Baghdadi, his first in almost a year, BBC reports.
In a speech, he calls on IS supporters to "persevere", despite the losses the group has suffered in Iraq and Syria.
The recording's authenticity could not be verified, but experts said the voice resembled that heard in other messages.
Although it is undated, there are references to recent events, including the detention of a US pastor in Turkey.
Russia claimed last year that it had probably killed Baghdadi in an air strike in Syria, but US commanders said they believed he was still alive and hiding in a remote area on the Syria-Iraq border.
In July, IS news outlets reported that Baghdadi's son Hudhayfah had been killed during an IS "commando operation" in the Syrian province of Homs.
Baghdadi - an Iraqi whose real name is Ibrahim Awwad Ibrahim al-Badri - has not been seen in public since he proclaimed the creation of a "caliphate" from the pulpit of the Great Mosque of al-Nuri in the northern Iraqi city of Mosul in July 2014.
His last audio message was released in September 2017, two months after Iraqi government forces recaptured Mosul and one month before IS militants were driven from their Syrian stronghold of Raqqa by a US-backed alliance of Kurdish and Arab fighters.
IS has now been defeated military in Iraq and most of Syria, and many of its fighters, planners, and senior doctrinal, security and military leaders have been killed.
In the audio message published late on Wednesday, August 22, Baghdadi appeared to try to shift attention away from his group's crippling losses.
"For the Mujahideen [holy warriors] the scale of victory or defeat is not dependent on a city or town being stolen or subject to that who has aerial superiority, intercontinental missiles or smart bombs," Reuters news agency quoted the recording as saying.
"Oh Caliphate soldiers... trust in God's promise and His victory... for with hardship comes relief and a way out," he added.
A UN report published last week said it was still estimated to have between 20,000 and 30,000 fighters across the two countries, including thousands of foreign nationals.
The group still controls small pockets of territory in the eastern Syrian province of Deir al-Zour, where it has been able to extract and sell some oil, and to mount attacks, including across the border with Iraq.
IS militants are also hiding out in Iraq's Anbar desert, the Ghadaf valley and Husseiniya.