WASHINGTON — The Islamic State group has taken advantage of weak and collapsing governments to expand its reach, and remains determined to attack the United States, the top U.S. intelligence official said Tuesday.

The Sunni extremist group, which is based in Syria and Iraq but has affiliates in Africa and Asia, has become the “preeminent global threat,” Director of National Intelligence James R. Clapper told the Senate Armed Services Committee in the annual “worldwide threats” hearing.

In what he called a “litany of doom,” Clapper outlined a diverse list of threats facing the United States, including terrorism, cyberattacks sponsored by China and Russia, drug trafficking, missile tests by Iran and continued enrichment of nuclear material by North Korea.

Violent extremists are active in about 40 countries, he said, including seven that are experiencing a collapse of central government authority and 14 others threatened by conflict.

“There are more cross-border military operations under way in the Middle East since any time since the 1973 Arab-Israeli War,” Clapper said.

He cited the conflicts in Iraq, Syria and Yemen as an example of the unstable conditions that Islamic State and other militant groups can use to expand, recruit and plot attacks against the U.S.

Clapper appeared later before the Senate Intelligence Committee, along with CIA Director John O. Brennan, FBI Director James B. Comey, National Security Agency Director Michael Rogers and Marine Lt. Gen. Vincent Stewart, director of the Defense Intelligence Agency, the Pentagon’s top spy agency.

The intelligence officials said North Korea continues to enrich fissile material that be used to fuel a nuclear bomb, adding to fears that Pyongyang is expanding its nuclear weapons program.