While there is little concrete evidence that North Korea’s nuclear program is advanced enough to be a direct threat to the United States, the secretive regime has become increasing beligerent in its threats over the past several months, and U.S. officials say it would be better to take precautions.

On Friday, Defense Secretary Chuck Hagel cited three recent developments that prompted the Obama administration to act:

A nuclear test in February that was widely condemned.

Pyongyang’s launch in December of a rocket that put a satellite into space and demonstrated mastery of some of the technologies needed to produce a long-range nuclear missile.

A public display by North Korea of a road-mobile intercontinental ballistic missile, the KN-08, which Navy Adm. James Winnefeld Jr., vice chairman of the Joint Chiefs of Staff, has said has the potential to reach the U.S.

Adding to concerns, North Korea recently nullified a 1953 truce with South Korea and threatened a pre-emptive strike against the United States.

Iran is also considered to be a potential nuclear threat by some, but its program is not believed to be extensively advanced.