US House Speaker Paul Ryan picked North Korea as one of the four biggest threats facing the United States, saying the communist nation is churning out anti-American invective while testing nuclear weapons and missiles.

"We are living in very dangerous times. ISIS still threatens our troops abroad and inspired terrorism here at home. North Korea continues to spew belligerent, anti-American rhetoric while testing long range missiles and nuclear devices," Ryan said in a speech at the American Israel Public Affairs Committee Policy Conference Monday evening.

Ryan said Iran is fanning the "flames of sectarian welfare in the Middle East while marching toward a nuclear weapons capability" while Russia remains an "ever-present threat to the post-Cold War order."

"In the coming years, dictators will rise and dictators will fall. Geopolitical landscapes will shift. Threats to our nation will evolve. But as I look out over this vast horizon of uncertainty, I remain optimistic and so should you," he said.

Concerns about North Korean threats have increased in the US as Pyongyang kept up testing of its weapons programs as well as bellicose rhetoric since leader Kim Jong-un threatened to test-fire an intercontinental ballistic missile apparently capable of reaching the US. (Yonhap)