IS's Al-Furqan Foundation started promoting the announcement at midday Wednesday.
"Coming Soon ... By the Willingness of Allah the Almighty," the announcement said, without sharing details.
In first significant announcement since Baghdadi's death ISIS teases a forthcoming release from its Al Furqan media foundation- the media wing responsible for the most important releases (such as the Baghdadi video and audio earlier this year)
View image on Twitter
7:34 PM - Oct 30, 2019
Twitter Ads info and privacy
21 people are talking about this
The SITE Intelligence Group, which monitors jihadist communications, said supporters quickly began distributing the poster on social media platforms, with some expressing hope that Baghdadi was still alive while others were preparing to celebrate his martyrdom.
IS official media operatives have been issuing their usual news updates on operations in Syria, Iraq and around the world, but they have been silent so far about the fate of Baghdadi, who was killed by U.S. special forces in a raid on a compound in Barisha in Syria's Idlib province.
U.S. President Donald Trump confirmed Baghdadi's death in a White House speech the same day.
U.S. officials also confirmed the death of IS spokesman Abu Hassan al-Muhajir in a follow-on operation a day later in Jarablus, near Syria's border with Turkey.
Impact of killings
Trump and U.S. Defense Secretary Mark Esper have described the death of Baghdadi and one of his top lieutenants as a significant blow to the terror organization, while promising to hunt down other top officials.
But a top counterterrorism official Wednesday warned that the impact, while significant, might be limited.
"It's absolutely fair to say it will be a morale hit," Russell Travers, acting director of the U.S. National Counterterrorism Center, told lawmakers.
"Nevertheless, the ideology continues, the resonance continues, and that is a strategic concern for us," he said, adding that when it comes to IS leadership, "it's a deep bench" and that a new leader most likely will be announced in the coming days or weeks.
"This is a bureaucracy that's pretty good at doing succession planning," Travers said.
Travers, testifying before the House Homeland Security Committee along with the director of the FBI and the acting director of the Department of Homeland Security, further warned that IS remained a capable and potent organization.
He said the terror group still commanded at least 14,000 fighters across Syria and Iraq, many of them operating in diffuse and clandestine cells that continue to launch attacks.
Those numbers also could get a boost from IS fighters who escaped from makeshift prisons run by the formerly U.S.-backed Syrian Democratic Forces, most of them getting free during the initial days of Turkey's military incursion in northeastern Syria.
"Our expectation is that the vast majority of the individuals who escaped, more likely than not, were Syrian and Iraqi, and will be looking to stay in the region. "They will be incorporated into the ISIS insurgency in all likelihood, and we could well see them serve as suicide bombers," Travers said, using an acronym for the group.
U.S. counterterrorism officials also expressed concern that some of them could be used in renewed attacks on the SDF-run prisons, as well as on displaced- persons camps housing tens of thousands of IS wives, children and other family members.
In the last message before his death, Baghdadi last month called on IS followers to free members of the group who had been captured or imprisoned.
"For your brothers and sisters, make [an] effort in saving them and destroying the gates that imprison them," Baghdadi said in the Sept. 16 audio recording.
"I assume that we will see some of that," Travers said Wednesday. "Those prisons are vulnerable."
FBI Director Christopher Wray also warned of indications that IS was preparing to make increased use of women and children.
"We know that ISIS has started to take advantage of women in operational planning and trying to recruit youth, some of them in these displacement camps," Wray said. "That's going to present all kinds of problems for us and our partners."