WASHINGTON—President Trump revealed Tuesday in his speech to Congress that the U.S. had taken custody of an Afghan involved in planning the deadly 2021 suicide attack at the Kabul airport that Trump has called “the most embarrassing moment in the history of our country.”

A senior member of the Islamic State branch based in Afghanistan was turned over to U.S. authorities by Pakistan and was being brought to the U.S. for prosecution, Trump said. U.S. officials identified him as Muhammad Sharifullah.