ERBIL, Iraq -- The shadowy leader of the Islamic State of Iraq and Syria, or ISIS, has released a new message urging his followers to keep up the fight for Mosul as they defend the city against a major offensive aimed at routing the militants from their last urban stronghold in Iraq.

Abu Bakr al-Baghdadi’s rallying cry came in a sermon-like recording, more than half an hour long, distributed by the militant group’s al-Furqan media arm late on Wednesday. It was not clear when the recording was produced. Al-Baghdadi’s whereabouts are unknown.

Iraqi special forces stormed into Mosul’s eastern outskirts on Tuesday after two weeks of advances through surrounding ISIS-held territory. They continued to consolidate their foothold in the eastern district of Gogjali despite a pair of attempted car bomb attacks on their positions Thursday.

The city of more than one million people and the surrounding territory fell to ISIS fighters during the militant group’s surprise attack in June 2014. Al-Baghdadi visited the city soon after the takeover, and from inside Mosul declared an Islamic caliphate that at one point covered nearly a third of Iraq and Syria.

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In his recording, al-Baghdadi rallies his fighters - especially in Mosul - and calls on them to obey orders while remaining resilient and steadfast.

“Oh you who seek martyrdom! Start your actions! Turn the night of the disbelievers into day,” he says, according to a translation provided by the SITE Intelligence Group, a U.S. organization that monitors militant activity online, which reported the al-Baghdadi recording first.

“Totally decimate their territories, and make their blood flow like rivers,” al-Baghdadi also says.

U.S. State Department spokesman Mark Toner said there was no reason to doubt the authenticity of the tape, CBS News correspondent Margaret Brennan reports.

“We’ll keep the pressure on them, and no audiotape is going to change that,” Toner said.

He then said Raqqa, the de facto capital of the militants’ self-proclaimed caliphate, was next.

Hours after al-Baghdadi’s call, an explosives-laden vehicle sped out of an ISIS-controlled area in Mosul and attacked Iraqi special forces positioned in the city’s easternmost Gogjali neighborhood on Thursday. The special forces fired a rocket that blew up the car, killing the attacker.

A second suicide attacker also emerged from the same area, the more central Samah district, Brig. Gen. Haider Fadhil said, but that vehicle managed to get away. ISIS fighters were also using explosives-laden drone aircraft, he said, adding that the militants had deployed two since the previous night but that both had been destroyed.

Troops in Mosul are stationed in the far east of the city, and have yet to push deep into the densely packed urban areas less than a mile away.

Iraqi forces continued to consolidate their gains into the evening, hunting for any ISIS fighters who may have stayed behind, checking houses and streets for booby traps, and handling an influx of hundreds of people who fled ISIS-held territory deeper in the city.

The commander of the Joint Military Operation Command, Lt. Gen. Talib Shaghati, told reporters on Thursday that more than 5,000 civilians have been evacuated to nearby camps since Wednesday from Gogjali and surrounding areas.

Inside Gogjali, security forces fired into the air to disperse civilians who were standing in a line to receive aid materials distributed by the Ministry of Migration and Displacement, concerned that large groups of people could be targets of militant attacks.

In his recording, al-Baghdadi also urges ISIS militants elsewhere to carry out attacks in Saudi Arabia, whose leadership ISIS opposes, and Turkey, which has deployed troops and artillery north of Mosul and is training Sunni Arab and Kurdish forces there.

The recording was the reclusive al-Baghdadi’s first released message to supporters since Iraqi forces launched the decisive battle to retake Mosul, the country’s second-largest city, from ISIS.

Al-Baghdadi attempts to harness the feelings of Sunni disenfranchisement that preceded the 2014 ISIS takeover of Mosul, a largely Sunni city in Shiite-majority Iraq. Using a derogatory term for Shiites, he says followers of the Muslim sect want to drive “empty Iraq of Sunnis and replace them with the worst of people.”

He calls on fighters to “respond to all attacks,” and to “target all in their media and forces, and all who belong to them.”

The audio message could not be independently verified, though the speaker’s voice and style of delivery resembled previous recordings of al-Baghdadi.

ISIS is fighting to hold Mosul as Iraqi forces and allied Kurdish forces advance on the city from multiple directions with U.S.-led coalition support. It is the Iraqi military’s largest offensive since the 2003 U.S.-led invasion.

Iraqi forces have proceeded cautiously since breaching Mosul’s eastern outskirts this week. They have yet to move into more densely populated areas that could lead to weeks, if not months, of clearing booby-trapped buildings and bloody house-to-house combat.

On Wednesday, residents in the easternmost district of Gogjali cautiously welcomed liberating Iraqi troops, with some raising white flags and flashing the “V’’ for victory sign. Men in the area celebrated by shaving the beards they were forced to grow under ISIS rule.

Meanwhile, Human Rights Watch warned that ethnic tensions were boiling over in Kirkuk, some 100 miles southeast of Mosul, where ISIS launched a surprise attack late last month that resulted in gun battles that lasted two days and killed at least 80 people.

In a statement, the New York-based group said that Kurdish authorities in the city have been ejecting Arab residents and Arab internally displaced people there since the attack, without explanation and in actions it considers “discriminatory.”

“Forcing families out of their homes and into the streets or to unsafe parts of the country is a serious violation of their rights and does nothing to strengthen Iraq’s political cohesion,” said Lama Fakih, the group’s deputy Middle East director.