WASHINGTON (AP) — President Joe Biden has vowed to keep up airstrikes against the Islamic extremist group whose suicide bombing at the Kabul airport killed scores of Afghans and 13 American service members. He warned another attack was “highly likely” and the State Department called the threat “specific” and “credible.” The Pentagon said the remaining contingent of U.S. forces at the airport, now numbering fewer than 4,000, had begun their final withdrawal ahead of Biden’s deadline for ending the evacuation on Tuesday. After getting briefed on a U.S. drone mission in eastern Afghanistan that the Pentagon said killed two members of the Islamic State group’s Afghanistan affiliate early Saturday, Biden said Saturday the extremists can expect more.