BEIRUT, Lebanon — Five years ago, Abu Bakr al-Baghdadi mounted the pulpit of a mosque in Iraq to declare himself the head of a rapidly expanding terrorist organization.
Since then, his group, the Islamic State, has transfixed the world with its apocalyptic violence while he has remained a mystery. Spottings were rare. Rumors swirled that he was wounded or dead. The United States put $25 million on his head and still failed to find him.
On Monday, he reappeared, leaning on a cushion with an assault rifle at his side, in a video seeking to rally his followers after the loss of the group’s territory in Iraq and Syria and its execution of one of the deadliest terrorist attacks in years, on Easter in Sri Lanka.
“Our battle today is a battle of attrition, and we will prolong it for the enemy, and they must know that the jihad will continue until Judgment Day,” he said in the video.
The message he intended to send was clear, analysts said: The Islamic State still exists, he is still in charge, and its international network of militants will continue to launch painful, unpredictable attacks. If he felt compelled to reveal himself now, after years in hiding, they said, it was to reassert his authority in the face of a punishing loss in Syria.
“Baghdadi has remained off the grid for so long that his sudden appearance will very likely serve as both a morale boost for ISIS supporters and remaining militants and as a catalyst for individuals or small groups to act,” said Colin P. Clarke, a senior fellow at the Soufan Center, a research organization for global security issues. “He is essentially reasserting his leadership and suggesting that he sits atop the command-and-control network of what remains of the group, not only in Iraq and Syria, but more broadly, in its far-flung franchises and affiliates.”
It was unclear when or where the video was recorded, but the parts that refer to recent events, like the Sri Lanka attack, are addressed in audio, not video, suggesting that it may have been recorded weeks ago with newer audio portions added later.
Much has changed for the Islamic State since Mr. al-Baghdadi appeared at Al Nuri Grand Mosque in the Iraqi city of Mosul in 2014. It was not just a militant group, he said, but a state that would be ruled according to the group’s extreme ideology.
That vision drew in tens of thousands of adherents from across the world, who populated an Islamist proto-state the size of Britain, stretching across Iraq and Syria with millions of people under its rule.
Now that territory is gone, after a four-year battle that ended in defeat last month at the hands of American-backed forces in the town of Baghuz, Syria.
Mr. al-Baghdadi acknowledged that loss in the video, an 18-minute infomercial released by an Islamic State media group on Monday and distributed by the SITE Intelligence Group. Seated cross-legged on the ground in an Arab-style sitting room, he calmly told a group of unidentified followers that the battle was far from over.
“Truthfully, the battle of Islam and its people with the crusader and his people is a long battle,” he said. He called on his followers to continue pursuing their enemies “with all of their abilities.”
And he said that the attack in Sri Lanka, in which at least 250 people were killed, was carried out “in revenge” for the Islamic State’s losses in Baghuz.
The video appeared at a critical inflection point for the Islamic State.
Despite claims that the loss of the so-called caliphate in Iraq and Syria had vanquished the group, it is believed to still have thousands of fighters there who have gone underground.
And as it lost territory in the Middle East, it has expanded abroad, turning to its international affiliates to carry out attacks farther afield. The coordinated bombing attack in Sri Lanka last week was one of the group’s deadliest, causing nearly twice as many deaths as the 2015 Paris attacks did.
Little is known about where and how Mr. al-Baghdadi spent the last five years. He has rarely appeared in public, and while he released occasional audio messages to guide to his followers, he never appeared in videos, the assumption being that such caution was considered necessary for his security.
The toll of those years was evident on Mr. al-Baghdadi’s face. In the video, he appears to have put on weight, and gray has streaked his beard, its ends dyed auburn with henna.
Even though he is one of the most wanted men on the planet, his whereabouts remains a mystery.
He is believed to be in hiding somewhere in the sparsely populated desert spanning the border along Iraq and Syria. American intelligence and counterterrorism officials say he eschews all electronic devices, which could identify his location, and probably communicates through a series of couriers.
He remains a top target for the Central Intelligence Agency and the military’s elite Joint Special Operations Command, which includes the Army’s Delta Force and the Navy’s SEAL Team 6. Occasional reports of his death notwithstanding, multiple attempts to kill him have failed.
The video appeared to be an effort to demonstrate that despite his group’s tremendous losses, it is still active and he is paying attention. He made passing references to the Israeli election and the toppling of longtime strongmen in Sudan and Algeria.
He also called out a number of the group’s leaders by name, mentioning fighters and operatives from Belgium, Australia and Saudi Arabia, reflecting the multinational organization the Islamic State has become.
“He’s exhibiting his ‘humble and modest’ self, unlike his last appearance where he is portrayed in what may be referred to as glorious standing, empowered by his group’s achievements, essentially standing at the top of the world,” said Laith Alkhouri, senior director of Flashpoint, which tracks global terrorism. “In today’s video, he appears defeated, but for his base he’s uplifting.”
The authenticity of the video could not be independently verified, but terrorism experts saw little reason to doubt that it was Mr. al-Baghdadi.
The Islamic State has not used frequent videos to create a cult of personality around its leader the way that Al Qaeda did with Osama bin Laden, but it could be heading in that direction, said Joshua Geltzer, who served as the senior director for counterterrorism on President Barack Obama’s National Security Council.
“I guess they considered the payoff worth it to show the organization hasn’t truly been defeated, even in its core manifestation,” he said.
Although the group has lost its territory in Iraq and Syria, it still claims a caliphate, which it considers a global project.
Hinting at the group’s global ambitions, the video ended with a follower handing Mr. al-Baghdadi files in plastic covers about the group’s different “states,” in Yemen, Somalia, Turkey and elsewhere.