Donald Trump’s national security adviser John Bolton says North Korea not taking steps towards denuclearization

U.S. President Donald Trump’s national security adviser John Bolton said North Korea has not taken steps towards denuclearizing the Korean peninsula despite an agreement between the president and Kim Jong Un.

Speaking to Fox News on Tuesday, Bolton said the U.S. has lived up to the agreement made between the two leaders in June, at the historic Singapore summit.

READ MORE: North Korea has renewed activity at missile production centre

“It’s the performance we need from North Korea,” Bolton said. “It’s just North Korea that has not taken the steps we feel necessary to denuclearize.”

On Monday, North Korean state media urged the U.S. to drop sanctions after the country demonstrated good faith by ending nuclear weapons testing and returning the remains of U.S. troops killed in the 1950-53 Korean War.

WATCH: Trump says he stopped missiles being launched in Korea

1:49 Trump says he stopped missiles being launched in Korea

“The idea that we are going to relax the sanctions just on North Korea’s say-so isn’t under consideration,” Bolton said. “We are going to continue to apply maximum pressure to North Korea until they denuclearize just as we are to Iran.”

Last week, U.S. spy satellites detected renewed activity at the North Korean factory that produced the country’s first intercontinental ballistic missiles capable of reaching the United States, a senior U.S. official told Reuters.

READ MORE: Pompeo accuses North Korea, Russia of continuing to violate U.N. sanctions

Photos and infrared imaging indicate vehicles moving in and out of the facility at Sanumdong, but do not show how advanced any missile construction might be, the official told Reuters on condition of anonymity because the intelligence is classified.

WATCH: Remains of U.S. servicemen killed in Korea loaded onto military plane

3:37 Remains of U.S. servicemen killed in Korea loaded onto military plane

Following the June summit, Trump declared that North Korea no longer posed a nuclear threat. Kim committed in a broad summit statement to work toward denuclearization, but Pyongyang has offered no details as to how it might go about that and subsequent talks have not gone smoothly.

WATCH: Pompeo says U.S. is engaged in ‘patient diplomacy’ with North Korea

1:38 Pompeo says U.S. is engaged in ‘patient diplomacy’ with North Korea

Last week, Trump thanked Kim “for keeping your word” and sending home the remains of U.S. soldiers. The president also said he received a new letter from the North Korean dictator and hinted at a possible meeting between the two.

“I am not at all surprised that you took this kind action. Also, thank you for your nice letter – l look forward to seeing you soon!” Trump tweeted.

READ MORE: U.S. State Secretary won’t specify timeline of denuclearization of North Korea

Bolton told Fox News there were no plans in place for a meeting between the two leaders, but said Trump was “prepared to meet at any point.”

“But what we really need is not more rhetoric, what we need is performance from North Korea on denuclearization,” the security adviser said.

–with a file from Reuters