ACHIN, Afghanistan—Afghan forces and U.S. airstrikes have dislodged Islamic State from its main stronghold in Afghanistan’s eastern province of Nangarhar, according to Afghan military and government officials.

Ground forces—led by the Afghan army and backed by police and paramilitary groups—pushed into Achin district, the group’s main base, just over a week ago as part of a continuing military operation, dubbed “Eagle 18,” against the extremist group.

...