The statement did not explain the reason for the long delay. The United States is not always sure who exactly has been killed in counterterrorism operations conducted from a distance, including by a drone strike, and confirmation can sometimes come later through new intelligence such as intercepted conversations or interrogations.

The announcement also comes as Mr. Trump faces intense criticism from national security experts, many of them Republicans, over his failure to prevent Turkey from invading northeastern Syria to attack Syrian Kurdish fighters. Those Kurdish fighters have been the major ground ally in Syria for the campaign against the Islamic State. Many military and intelligence officials believe the Turkish action could make it easier for the Islamic State, or ISIS, to regenerate as the Kurds turn their attention toward their Turkish enemies.

“This is important, but it’s not news,” said Joshua A. Geltzer, who served as a senior director for counterterrorism on the National Security Council in the Obama administration.

“Credible reports have been indicating Asiri is dead for over a year,” Mr. Geltzer added. “So this announcement appears deliberately designed to portray Trump as tough on terrorism in a week when he’s proving the opposite — when he’s abandoning key U.S. partners in the fight against ISIS and thus directly raising the terrorist threat to Americans.”

Writing in The Washington Post soon after reports of Mr. Asiri’s death last year, the former deputy director of the Central Intelligence Agency, Michael J. Morell, said that, if confirmed, “he would be the most significant international terrorist removed from the battlefield since Osama bin Laden.”