Story highlights Secretary of State John Kerry says al-Maliki made an ''honorable decision''

U.S. carries out airstrikes against ISIS targets northeast of Irbil

U.S. military assessment finds there are far fewer Yazidis trapped than originally thought

Prime Minister Nuri al-Maliki gave up the fight Thursday to keep his post, clearing the way for a new leader that many hope can hold Iraq together as the country battles brutal extremist fighters.

In a televised address, al-Maliki withdrew his candidacy for a third term and endorsed the Prime Minister-designate , bringing to an end a political battle that just days ago saw him vow to hold onto power as he ordered tanks into the streets.

"I announce to you today that I am withdrawing my candidacy in deference to my brother, Haider al-Abadi, in the highest interest of the country," he said.

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The news -- first flashed on state television -- follows mounting pressure, at home and abroad, for al-Maliki to step aside and make way for someone to bridge the sectarian divide that many accuse him of fomenting.

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The move comes at a critical time in Iraq as Sunni fighters with the so-called Islamic State, formerly known as the Islamic State of Iraq and Syria, force hundreds of thousands from their homes as they seize large swaths of land.

Al-Maliki's announcement came the same day that U.S. President Barack Obama declared the ISIS siege that trapped thousands in the Sinjar Mountains over, but warned the crisis is far from solved.

While humanitarian airdrops and U.S. airstrikes saved those stranded from starving and provided safe passage off out of the mountains, the Yazidis arrived by the thousands at camps in and outside Iraq.

Al-Maliki will continue to serve as the country's caretaker Prime Minister -- as well as its top military commander -- until al-Abadi forms a new government.

Al-Maliki's acquiescence was a turnaround for the man, who in recent days called the appointment of al-Abadi unconstitutional and said he would not step down.

He had gone so far as to file a lawsuit in federal court to stop the formation of a new government and ordered tanks and soldiers loyal to him into the streets of Baghdad, raising concerns of a possible coup.

But with world leaders, diplomats, members of his own political party and the country's most revered Shiite cleric pressuring him to step down, al-Maliki gave up the fight.

Calling it in an "honorable decision" by al-Maliki, U.S. Secretary of State John Kerry urged al-Abadi to move quickly to form the government, saying it is essential to pulling the country's various ethnic and religious groups together to fight a common enemy in ISIS.

While Iraq works to seat a new government, Obama said in a televised address on Thursday that the United States will continue to conduct airstrikes to protect U.S. personnel and facilities.

The United States carried out airstrikes Thursday against three ISIS targets northeast of the Kurdish regional capital of Irbil, according to the U.S. Central Command.

The targets were U.S.-manufactured mine-resistant ambush-protected vehicles, more commonly known as MRAPs, and other armored vehicles being driven by ISIS fighters. The vehicles are believed to have been seized by ISIS after it routed Iraqi troops in northern Iraq.

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Photos: Iraqi refugees fleeing ISIS Photos: Iraqi refugees fleeing ISIS Iraqi refugees fleeing ISIS – A Yazidi family from Sinjar cleans a spot for themselves in a derelict building that houses more than a thousand other refugees on Thursday, August 14, in Zakho, Iraq. Hide Caption 1 of 17 Photos: Iraqi refugees fleeing ISIS Iraqi refugees fleeing ISIS – A woman and child sit in the makeshift housing on Thursday. Hide Caption 2 of 17 Photos: Iraqi refugees fleeing ISIS Iraqi refugees fleeing ISIS – A Yazidi woman holds her baby while crossing Peshkhabour bridge from Syria back into Kurdish-controlled Iraq on Tuesday, August 12. Hide Caption 3 of 17 Photos: Iraqi refugees fleeing ISIS Iraqi refugees fleeing ISIS – Entire families carry nothing but the clothes on their back. Some are barefoot. And not everyone who set out on the arduous journey survived. Hide Caption 4 of 17 Photos: Iraqi refugees fleeing ISIS Iraqi refugees fleeing ISIS – The militant group ISIS, which now calls itself the Islamic State, executes civilians who don't adhere to its version of Sunni Islam. Hide Caption 5 of 17 Photos: Iraqi refugees fleeing ISIS Iraqi refugees fleeing ISIS – Yazidis fled into the barren and windswept Sinjar Mountains more than a week ago after ISIS captured their town. Hide Caption 6 of 17 Photos: Iraqi refugees fleeing ISIS Iraqi refugees fleeing ISIS – Descendants of Kurds and followers of an ancient pre-Islamic religion, Yazidis are one of Iraq's smallest minorities, and have been persecuted for centuries, but they have a strong sense of community. Hide Caption 7 of 17 Photos: Iraqi refugees fleeing ISIS Iraqi refugees fleeing ISIS – According to some accounts, Syrian Kurds also helped people use parts of northeastern Syria under their control to reach Kurdish areas of northern Iraq. Hide Caption 8 of 17 Photos: Iraqi refugees fleeing ISIS Iraqi refugees fleeing ISIS – A young refugee carries a disabled man across the bridge. Hide Caption 9 of 17 Photos: Iraqi refugees fleeing ISIS Iraqi refugees fleeing ISIS – Thousands trudge across a river to seek humanitarian aid in Syria. Hide Caption 10 of 17 Photos: Iraqi refugees fleeing ISIS Iraqi refugees fleeing ISIS – A number of those who made the treacherous trek off the mountain told CNN that PKK fighters control parts of the mountain, and they fed and protected them from ISIS. Hide Caption 11 of 17 Photos: Iraqi refugees fleeing ISIS Iraqi refugees fleeing ISIS – A Kurdish border guard watches while people cross. Hide Caption 12 of 17 Photos: Iraqi refugees fleeing ISIS Iraqi refugees fleeing ISIS – A senior Kurdish official estimated that as many as 70,000 people remain trapped on Mount Sinjar, and that at least 100 have died so far from dehydration and the heat. CNN could not independently confirm those estimates. Hide Caption 13 of 17 Photos: Iraqi refugees fleeing ISIS Iraqi refugees fleeing ISIS – A man weeps after been reunited with his family. Hide Caption 14 of 17 Photos: Iraqi refugees fleeing ISIS Iraqi refugees fleeing ISIS – A Kurdish Peshmerga stands in front of the bridge. Hide Caption 15 of 17 Photos: Iraqi refugees fleeing ISIS Iraqi refugees fleeing ISIS – Children rest after arriving back into Kurdish-controlled Iraq. Hide Caption 16 of 17 Photos: Iraqi refugees fleeing ISIS Iraqi refugees fleeing ISIS – A little girl was seen crossing the bridge by herself. The United States is sending more troops to northern Iraq, a move that U.S. officials told CNN is necessary to help in the rescue of tens of thousands of Yazidis trapped in the mountains. Hide Caption 17 of 17

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Also, there were reports that ISIS fighters were advancing south and west of Kirkuk, about 240 kilometers (149 miles) north of Baghdad.

At the same time, Obama urged Iraq's Shiite-dominated government to seize "the enormous opportunity of forming a new inclusive government" under al-Abadi.

"He still has a challenging task in putting a government together, but we are modestly hopeful that the Iraqi government situation is moving in the right direction," he said.

The new battleground in Iraq appeared to be spreading to the south and west of Kirkuk, where ISIS fighters occupied four towns to the south and west of Kirkuk, according to Hisham al-Hashimi, a researcher at the Journalistic Freedom Observatory.

According to his sources in the field, there was fighting ongoing between ISIS and Kurdish fighters, known as Peshmerga, in the town of Tuz Khurmatu. The town is home to a number of Turkmen, an ethnic minority in Iraq.

The United Nations estimates that more than 400,000 people have been driven from their homes since June, when ISIS swept across the border from Syria into Iraq.

Of those displaced, more than 200,000 have poured into northern Dohuk province in recent weeks, where refugee camp populations have swelled since ISIS began its assault against Yazidis, Christians, Kurds and Shiites.

Thousands of other refugees sought protection inside the northern Kurdish region of Iraq.

"To be blunt, we don't have housing for all of them. We don't have shelter," a spokesman for the U.N. human rights commissioner, Edward Colt, said at a camp near the Peshkhabour bridge where Iraqis are entering the area. "Thousands of tents are being erected as we speak."

Yazidi refugees were also fleeing across the Iraqi border into Syria.

As of Thursday, there were about 15,000 Yazidi refugees from Iraq who arrived at the Newroz camp in Syria, the U.N. refugee agency said. Thousands more are arriving, the agency said.

The Yazidis fled last week in the Sinjar Mountains as ISIS overran the city of Sinjar.

A senior commander said ISIS fighters abducted more than 100 Yazidi women and children from the community.

The ISIS commander, who has knowledge of the events that unfolded, said the fighters killed a large number of men when they took over the town more than a week ago.

"At that time, they took Yazidi women and children, and I can confirm those women and children have entered Mosul," the commander said by telephone. "...The Islamic State is taking this opportunity to call them to Islam."

While CNN cannot independently confirm the claim, it follows reports by survivors who describe ISIS fighters grabbing families and separating the men from the women and children.