DOVER, Del. — President Biden on Sunday paid his respects to the 13 Americans killed in last week's suicide bombing in Afghanistan as his military leaders tried to avert more carnage in the final days of a chaotic withdrawal from the country, carrying out a strike on a vehicle in Kabul that officials said posed a terrorist threat.

Biden flew to an Air Force base here to receive the fallen service members, whose remains were returned to the United States on Sunday morning. He first met privately with their family members, including some who have expressed anger at him, and then watched quietly as flag-draped cases transporting the bodies were carried off a plane — a somber moment during the most volatile crisis of his presidency.

Thousands of miles away, U.S. officials worked with urgency to prevent more American casualties, as they move to conclude their evacuation mission by Tuesday. Defense Department officials said the military carried out a drone strike on a vehicle in Kabul that posed an "imminent" threat to Hamid Karzai International Airport. The Thursday suicide bombing that killed 13 Americans and 170 civilians, for which the Islamic State affiliate known as ISIS-K claimed responsibility, happened at an airport entrance.