Donald Trump is watching North Korea's activities very carefully, John Bolton said.

U.S. President Donald Trump has an understanding with North Korean leader Kim Jong Un that Pyongyang will not launch intercontinental-range ballistic missiles, and the United States is watching North Korean missile tests very carefully, Trump's national security adviser John Bolton told Fox News Channel on Tuesday.

"It looks like it's a testing series that they want to get this missile fully operational," Bolton, speaking from Peru's capital Lima, said about the North Korean missile launches over the past two weeks.

"They appear to be ballistic missiles. The president and Kim Jong Un have an understanding that Kim Jong Un is not going to launch longer range, intercontinental range ballistic missiles, and so I think the president is watching this very very carefully."