Despite the military defeat of the Islamic State (IS) in Iraq and most of Syria, the extremist group still has around 20,000 to 30,000 militants in the two countries, according to a United Nations report.
The report circulated on August 13 said the estimate came from governments it did not identify. It includes a "significant component" of foreign fighters.
The militants were equally divided between Iraq and Syria, said the report to the Security Council by experts monitoring sanctions against the Islamic State and Al-Qaeda.
Many of the key IS operatives were being relocated to Afghanistan, where the group has between 3,500 and 4,000 fighters and is growing, the experts said.
The militant group led by Abu Bakr al-Baghdadi also has significant affiliated supporters in Libya, Southeast Asia, and West Africa.
Islamic State overran large parts of Iraq and Syria in 2014, but by January 2018, the group was confined to small pockets of territory in Syria.
According to the UN report, IS "is still able to mount attacks inside Syrian territory. It does not fully control any territory in Iraq, but it remains active through sleeper cells."
The flow of foreign fighters to IS in Syria and Iraq has come to a halt, the experts said, but "the reverse flow, although slower than expected, remains a serious challenge."
They said Al-Qaeda's global network also "continues to show resilience," with its affiliates and allies much stronger than the IS group in some spots, including Somalia, Yemen, South Asia, and Africa's Sahel region.