Ayotte: China could end North Korea situation 'tomorrow'

"The problem is we don't know what he's going to do," Ayotte said.

On Tuesday, North Korea told foreign visitors to the South that they risked involvement in a "merciless, sacred, retaliatory war" if they remained in the country.

It was the latest in a series of bellicose threats from the North, which in recent weeks has cut off economic and diplomatic ties and shifted missiles to its coast. But despite the rhetoric from Pyongyang, most foreign policy experts say the regime is unlikely to mount an actual military attack.

Still, the United States has responded with a series of military maneuvers, including moving Navy ships into the region, deploying a missile defense system in Guam, and performing military exercises near the border. Ayotte, a frequent critic of the Obama administration, said she was pleased by the White House response.

"North Korea has to understand our resolve, number one, that if they take any acts towards us or our allies, that we have assets in place that are going to respond … it's very important that our allies South Korea and Japan have our back," Ayotte said.