Islamic State leaders, the analysts found, were monitoring political developments in Western European nations and considering attacks that would inflame domestic divisions. Though its planning capabilities are limited now, the group has carried out reconnaissance of potential targets and has positioned explosives.

President Trump confidently predicted the group’s elimination when United States and allied forces took Baghuz, Syria, the last stronghold of the Islamic State’s caliphate, in late March. The report’s authors, though, say the group still has many fighters in Iraq and Syria who are able to move freely and carry out attacks.

Some 30,000 Islamic State foreign fighters and dependents may have survived the conflict and “will be of international concern for the foreseeable future,” the analysts said. “Some may join Al Qaeda or other terrorist brands that may emerge.”

European governments have estimated that around 5,000 to 6,000 of their citizens have traveled to Syria and Iraq to join extremist movements, most of them signing up with the Islamic State. While many were killed or detained, up to 40 percent are unaccounted for.

The radicalization of people held inside Europe’s prisons “remains a critical concern,” the report said, noting the first wave of returnees who had been jailed were expected to be released in the coming year.