Originally Published: 26 AUG 21 11:49 ET

Updated: 26 AUG 21 13:21 ET

By Kevin Liptak, CNN

(CNN) -- Terrorist explosions outside Kabul's international airport on Thursday that killed multiple US service members came after days of public and private warnings from President Joe Biden of a potential attack that could disrupt the massive airlift effort underway there.

The Pentagon said in a statement that "a number of US service members were killed in today's complex attack." The statement said a number of others were being treated for wounds.

Biden was attending a pre-scheduled meeting of his national security team at the White House when reports of the attack reached Washington. Inside the basement Situation Room, Biden was briefed on the incident by his team, according to White House officials.

The remainder of his schedule remained in flux as White House officials determined whether and when he should address the situation publicly.

US Defense Secretary Lloyd Austin, Secretary of State Antony Blinken and Joint Chiefs Chairman Gen. Mark Milley were all seen arriving for the meeting after 9 a.m. ET. Vice President Kamala Harris also took part in the meeting via video conference while she was in the air traveling between Vietnam and Guam where she has now landed.

The President's meeting with visiting Israeli prime minister Naftali Bennett at the White House scheduled for Thursday morning has been delayed, a US official said.

After Biden's meeting with his national security team concluded, he continued to be briefed in the Oval Office, according to the White House. The White House press briefing, initially scheduled for 12:00 p.m. ET, has been delayed and the President's virtual meeting with governors on Afghan refugees, which was scheduled for 3 p.m. ET, has been canceled.

US officials believe ISIS-K was likely behind the attack but are still working to confirm the terror group's involvement, according to a senior US official and another source briefed on initial assessments.

The Pentagon described the incident as "a complex attack that resulted in a number of US & civilian casualties."

And a Taliban spokesperson said it will take "every step to bring the culprits to justice" for the explosions near the airport, adding that 13 people are reported to have been killed and 52 wounded.

The explosions laid bare the risks to US troops and diplomats Biden has warned about for a week as a frantic evacuation effort at the airport gained speed. The pace of evacuations has slowed over the past two days as the security situation deteriorated.

The risks seemed to grow by the hour: the extremely high threat of a terror attack from ISIS caused the US, along with the UK and Australia, to warn people to move away from the airport gates late Wednesday eastern time.

The risk of potential terror attacks from the Islamic State affiliate operating in Afghanistan worried American and Western officials from nearly the moment it became clear that the Taliban would take over the country on August 15.

Once crowds began massing at the Hamid Karzai International Airport, the fear among officials monitoring the situation became acute of an attack meant to create mayhem and fear among those trying to escape the country.

Biden raised the possibility of an attack — not from the Taliban, but from the ISIS group — last Friday.

"We're also keeping a close watch on any potential terrorist threat at or around the airport, including from the ISIS affiliates in Afghanistan who were released from prison when the prisons were emptied," he said.

On Tuesday, explaining his decision to stick with an August 31 deadline for withdrawing all US troops from the country, Biden offered a more dire picture of the security threat.

"The longer we stay, starting with the acute and growing risk of an attack by a terrorist group known as ISIS-K, an ISIS affiliate in Afghanistan -- which is the sworn enemy of the Taliban as well -- every day we're on the ground is another day we know that ISIS-K is seeking to target the airport and attack both US and allied forces and innocent civilians," Biden said.

This story is breaking and will be updated.