"We can confirm that a number of US service members were killed in today's complex attack on Kabul airport," said spokesman John Kirby.

"A number of others are being treated for wounds," he said, calling it a "heinous attack."

The Pentagon declined to give figures, but Fox News and The Wall Street Journal reported that four marines were killed in the attack, which involved two bombs, one at the airport's Abbey Gate and one at a nearby hotel that had been used as a staging point for evacuations.

Ahead of the attack US and other coalition partners warned they had intelligence that the Afghan arm of the Islamic State group, the Islamic State-Khorasan (IS-K), was planning suicide bomb attacks on the airport.

They were the first US service members to be killed in Afghanistan since Washington signed an agreement with the Taliban in February 2020 to withdraw from the country.

In exchange for a commitment to pull out, the Taliban agreed to not carry out attacks on US or NATO troops.

More than 5,000 US troops are at the airport to provide security for the massive airlift that has taken close to 100,000 people, Afghans and foreign nationals, out of the country since April 14, fleeing the Taliban's seizure of power.

President Joe Biden earlier this week cited the ongoing security threat to the Hamid Karzai International Airport, particularly from IS-K, as a reason for sticking to his withdrawal deadline of August 31.

Thousands of Afghans and foreigners are still awaiting evacuation from the country.