ISIS leader Abu Bakr Al Baghdadi has released an audio message claiming the group is carrying out "daily operations" on different fronts.
Its release is five months after he appeared in a video when it was believed the world's most-wanted terrorist leader was injured in fighting.
In the new audio tape, Al Baghdadi says "daily operations are under way on different fronts" in regions such as Mali and the Levant, but he gives no specific times.
The extremist group leader appeared to call for his followers to free detained ISIS members and their families held in camps in Iraq and Syria.
"The prisons, the prisons, soldiers of the caliphate!" he said.
"Do your utmost to rescue your brothers and sisters and break down the walls that imprison them," he added in the message distributed by the Telegram app.
Rita Katz, an analyst and co-founder of the US Search International Terrorist Entities Intelligence Group, tweeted: "This new speech is titled, 'Do Deeds.'
"Baghdadi’s speech is heavy on religious content and comments on the second 'Battle of Attrition', indicating it was recorded recently," Ms Katz said, referring to 152 attacks ISIS claimed in 10 provinces between August 2 and 11.
"He calls on fighters to redouble efforts: preaching, media, military, security."
Last month the Amaq news agency reported that Al Baghdadi had named as his successor Abdullah Qardash, an Iraqi of Turkmen origin from the Telafar region near the northern Iraqi city of Mosul.
Earlier on Monday, Maj Gen Chris Ghika, the departing top UK commander in the US-led international coalition against ISIS, told Forces News that Al Baghdadi was not a threat.
"Although he holds an iconic status, because he was the person who stood on the balcony of Al Nuri Mosque in 2014 [when he declared the caliphate in Iraq and Syria], we don't really see him as somebody of great importance," Gen Ghika said.
"I am pretty confident Al Baghdadi will be killed or caught during this campaign."
The US government has placed a $25 million (Dh91.8m) bounty on his head.
In his last public message in April, Al Baghdadi said ISIS had launched a war of attrition ordained by God.
The announcement followed the defeat of the group by US-led Kurdish militia in eastern Syria and the killing of many of his lieutenants by US forces.
Unsubstantiated reports had described him as killed or wounded by US bombing, or living as a fugitive in Syria, Iraq or Libya.