An Islamic State offshoot based near the Afghan-Pakistan border is expanding to new areas, recruiting fighters and widening the reach of attacks in the region, members of the movement and Afghan officials said.

Some members of the so-called “Khorasan Province” of Islamic State claimed responsibility for the recent attack on a Sufi shrine in Pakistan that killed 90 people, and IS gunmen were blamed for the deaths of six local aid workers in the north of the country, far from their stronghold in eastern Afghanistan.

Any expansion would pose a new challenge for U.S. President Donald Trump, as he considers how many American troops to keep in Afghanistan where the main security threat remains the Taliban insurgency.

Trump has vowed to “totally destroy” the Middle East-based Islamic State, yet has spoken little of Afghanistan, where U.S. forces have been posted for 15 years.