"It is one in a series of successful strikes against ISIL leaders, including those responsible for finances and military planning, that make it harder for the group to operate," he added. Cook said the targeting of ISIS leaders and the plotters of overseas attacks would continue.
In the days after the strike on Aug. 30, Pentagon officials had cautioned that they awaited a final assessment that would confirm if he had actually been killed in the airstrike. Those assessments are made by the intelligence community using a combination of intercepted communications and other intelligence to make a final determination on the success of a strike.
Russia later claimed credit for the airstrike leading to an unusually blunt response from a U.S. official calling the Russian claim "a joke".
Al-Adnani was known primarily as the chief spokesman for ISIS, but he was also the driving force behind high-profile ISIS terror attacks like last November's deadly attack in Paris and the bombing at the airport in Brussels.