U.S. President Donald Trump said on Wednesday that other countries will need to take up the fight against Islamic State militants, citing Russia, Pakistan and Iran as examples.
Earlier this year, U.S.-backed forces reclaimed the last remaining territory once held by Islamic State militants in Syria. Since then however, there has been concern about the militant group gaining new strength in Iraq and Syria.
U.S. Secretary of State Mike Pompeo acknowledged on Tuesday that Islamic State militants are gaining strength in some areas but said the militant group's capacity to conduct attacks has been greatly diminished.
In Afghanistan, a deal between the Taliban and the United States for U.S. forces to withdraw from their longest-ever war could drive some diehard Taliban fighters into the arms of Islamic State, Afghan officials and militants say.
The Afghan affiliate of Islamic State, known as Islamic State Khorasan (ISIS-K), after an old name for the region, first appeared in eastern Afghanistan in 2014, and has since made inroads into other areas, particularly the north.
Trump also told reporters at the White House that if Europe does not take Islamic State fighters held as prisoners, he will have to release them into the countries from which they came, such as Germany and France.
Thousands of people, including men, women and children from more than 50 countries, are lingering in detention camps in northeastern Syria, held by the U.S.-backed Syrian Democratic Forces (SDF).
The group includes at least 2,000 suspected foreign fighters, many from Western countries, whose fates remain unresolved against a backdrop of protracted diplomacy.