WASHINGTON: Leaders of the Islamic State are determined to strike targets in the United States this year, senior intelligence officials have said, telling lawmakers that a small group of violent extremists will attempt to overcome the logistical challenges of mounting such an attack.

In testimony before congressional committees, Director of National Intelligence James Clapper and other officials described the Islamic State as the "pre-eminent terrorist threat." The militant group can "direct and inspire attacks against a wide range of targets around the world," Clapper said on Tuesday.

Marine Lt Gen Vincent Stewart, director of the Defense Intelligence Agency, said the Islamic State will probably conduct additional attacks in Europe and then attempt the same in the US. He said US intelligence agencies believe IS leaders will be "increasingly involved in directing attacks rather than just encouraging lone attackers."

Clapper also said al-Qaida, from which the Islamic State spun off, remains an enemy and the US will continue to see cyber threats from China, Russia and North Korea, which also is ramping up its nuclear program.

North Korea has expanded a uranium enrichment facility and restarted a plutonium reactor that could begin recovering material for nuclear weapons in weeks or months, Clapper said in delivering the annual assessment by intelligence agencies of the top dangers facing the country.

Clapper said that Pyongyang announced in 2013 its intention to refurbish and restart nuclear facilities, to include the uranium enrichment facility at Yongbyon and its plutonium production reactor, which was shut down in 2007. He said US intelligence had assessed that North Korea has expanded Yongbyon and restarted the plutonium production reactor there.

Clapper also told the Senate Armed Services and intelligence committees that North Korea has been operating the reactor long enough that it could begin to recover plutonium "within a matter of weeks to months."

Both findings will deepen concern that North Korea is not only making technical advances in its nuclear weapons program, following its recent underground test explosion and rocket launch, but is working to expand what is thought to be a small nuclear arsenal. US-based experts have estimated that North Korea may have about 10 bombs, but that could grow to between 20 and 100 by 2020.

North Korea on Sunday launched a rocket carrying an Earth observation satellite into space. The launch followed a Jan. 6 underground nuclear explosion that North Korea claimed was the successful test of a "miniaturized" hydrogen bomb. Many outside experts were skeptical and Clapper said the low yield of the test "is not consistent with a successful test of a thermonuclear device."

Clapper said that Pyongyang is also committed to developing a long-range, nuclear-armed missile that is capable of posing a direct threat to the United States, "although the system has not been flight-tested."