President Joe Biden on Sunday called the extraordinary fall of the Assad regime in Syria “a moment of risk” and “historic opportunity” while offering a blueprint for how the US plans to support the region.

Speaking at the White House in his first substantive comments since President Bashar al-Assad’s regime fell in the face of an astonishingly swift rebel offensive, Biden also announced the US had conducted dozens of airstrikes in Syria as it remains committed to preventing the resurgence of ISIS.

“It’s a moment of historic opportunity for the long-suffering people of Syria to build a better future for their proud country,” Biden said from the Roosevelt Room. “It’s also a moment of risk and uncertainty. As we all turn to the question of what comes next, the United States will work with our partners and the stakeholders in Syria to help them seize an opportunity to manage the risk.”

Biden vowed to support Syria’s neighbors during the transition and to protect US personnel in their continued mission against ISIS. The president said he plans to speak with his counterparts in the area “in the coming days” and that US officials will deploy to the region.

The US is prioritizing efforts to prevent the resurgence of ISIS, Biden said, adding that he is “clear-eyed about the fact that ISIS will try to take advantage of any vacuum to reestablish its capability to create a safe haven,” but starkly saying, “We will not let that happen.”

Biden noted those efforts include securing detention facilities where ISIS fighters are being held as prisoners, as well as “precision strikes” in Syria targeting ISIS.

As part of that effort, US forces on Sunday conducted dozens of airstrikes, striking more than 75 ISIS targets using Air Force assets including B-52 bombers, F-15 fighter jets and A-10 aircraft, according to US Central Command.

“There should be no doubt — we will not allow ISIS to reconstitute and take advantage of the current situation in Syria. All organizations in Syria should know that we will hold them accountable if they partner with or support ISIS in any way,” Gen. Erik Kurilla, commander of CENTCOM, said in a statement.

Biden’s comments come as President-elect Donald Trump — who takes the oath of office in just over six weeks — has urged a hands-off approach to the conflict, saying Saturday that the US should not get involved. Early Sunday, as rebel groups took Damascus, he said the regime’s fall showed the “weakened state” of Russia and Iran, both of which supported Assad.

“Assad is gone. He has fled his country. His protector, Russia, Russia, Russia, led by Vladimir Putin, was not interested in protecting him any longer,” Trump said in a post to social media.

Assad and his family fled to Moscow, where they were granted asylum, Russian state media said Sunday.

The Assad regime’s collapse represented a spectacularly fast fall from power for the Syrian dictator after a 14-year war, one that had been relatively stagnant until just last month. More than 300,000 civilians have been killed in more than a decade of war, according to the United Nations, and millions of people have been displaced.

Biden pledged in his remarks to engage with Syrian groups as the country transitions toward an “independent, sovereign … new government that serves all of Syria.”

“This process will be determined by the Syrian people themselves,” Biden said. “The United States will do whatever we can to support them, including through humanitarian relief, to help restore Syria after more than a decade of war and generation of brutality by the Assad family.”

A senior administration official echoed that sentiment to CNN on Sunday, saying the US will be “engaging with the broad spectrum of Syrian society, opposition groups, groups on the ground in Syria, exile groups.”

US Secretary of State Antony Blinken echoed Biden’s comments, saying in a statement Sunday that the US strongly supports a peaceful transition of power to an accountable Syrian government.

“During this transitional period, the Syrian people have every right to demand the preservation of state institutions, the resumption of key services, and the protection of vulnerable communities,” Blinken said.

Biden warned in his remarks that the US will “remain vigilant” and closely watch the rebel groups’ actions. The key rebel group leading the offensive, Hayat Tahrir al-Sham, or HTS, has been designated by the US as a terrorist organization. A senior US official told CNN on Sunday that the US believes significant portions of HTS maintain strong links to ISIS.

“We take a note of statements by the leaders of these rebel groups in recent days, and they’re saying the right things now, but as they take on greater responsibility, we will assess not just their word, but their actions,” Biden said.

Abu Mohammad al-Jolani, who heads HTS, declared victory for the “entire Islamic nation” on Sunday in his first public remarks since the rebel-led coup, which he said “marks a new chapter in the history of the region.”

He said the armed opposition ultimately plans to form a government defined by institutions and a “council chosen by the people.”

The senior Biden administration official said Sunday the White House has also “been concentrated” over the last week on the issue of any remaining chemical weapons in the Syria, calling it a “top-tier priority.” The senior official did not envision a scenario in which the administration would put US forces on the ground to deal with the chemical weapons.

Rebels have asked the international community to help dispose of the weapons. Multiple investigations by fact-finding teams from the Organization for the Prohibition on Chemical Weapons have previously concluded the Syrian government forces were responsible for a series of chemical attacks during the civil war.

Blinken said the US will support international efforts to hold the Assad regime and its backers accountable for atrocities perpetrated against the Syrian people, including “the use of chemical weapons and the unjust detention of civilians such as Austin Tice.”

Biden also reiterated his commitment to bringing home freelance journalist Austin Tice, who has been held in Syria since 2012. “We remain committed to returning him to his family,” Biden said in his Sunday remarks, adding, “We believe he’s alive. We think we can get him back.”

When asked by reporters at the White House whether he would approve an operation to retrieve Tice, Biden said, “We want to get him out. We have to identify where he is.”

In a statement to CNN, Tice’s parents, Marc and Debra Tice, said, “We are eagerly anticipating seeing Austin walk free. We are asking anyone who can do so to please assist Austin so he can safely return home to his family.”

On Friday, CNN reported that Debra Tice said her son “is being cared for, and he is well,” citing what she called a “significant source that has already been vetted all over our government.”

US officials reached out to Syrian opposition forces on Thursday about Austin Tice, hoping to learn more about his whereabouts. The FBI said Sunday it is still offering a reward of up to $1 million for information that can lead to Tice’s safe return.

This story and headline have been updated with additional developments.

CNN’s Jim Sciutto, Natasha Bertrand, Brian Stelter, Michael Conte, Alex Marquardt, Evan Perez and Philip Wang contributed to this report.

CNN