Washington (CNN) Months after President Donald Trump declared that North Korea no longer poses a nuclear threat to the US, Secretary of State Mike Pompeo said that the country remains a threat ahead of a planned summit between Trump and North Korean leader Kim Jong Un this week.

"Do you think North Korea remains a nuclear threat?" CNN's Jake Tapper asked Pompeo Sunday on "State of the Union."

"Yes," Pompeo replied.

"But the President said he doesn't," Tapper said.

"That's not what he said ... I know precisely what he said," Pompeo said.

"He tweeted : 'There is no longer a nuclear threat from North Korea,'" Tapper said.

"What he said was that the efforts that had been made in Singapore -- this commitment that Chairman Kim made -- have substantially taken down the risk to the American people. It's the mission of the Secretary of State and the President of the United States to keep American people secure. We're aiming to achieve that," Pompeo said.

In June, Trump, having just returned to Washington from a historic summit with Kim in Singapore, tweeted, "There is no longer a Nuclear Threat from North Korea."

Just landed - a long trip, but everybody can now feel much safer than the day I took office. There is no longer a Nuclear Threat from North Korea. Meeting with Kim Jong Un was an interesting and very positive experience. North Korea has great potential for the future! — Donald J. Trump (@realDonaldTrump) June 13, 2018

In a separate tweet, the President said that North Korea is "no longer" the US' "biggest and most dangerous problem," telling Americans and the rest of the world they can "sleep well tonight!"

Before taking office people were assuming that we were going to War with North Korea. President Obama said that North Korea was our biggest and most dangerous problem. No longer - sleep well tonight! — Donald J. Trump (@realDonaldTrump) June 13, 2018

This week, Trump is set to meet with Kim for a second summit in Vietnam in which he will likely try to convince Kim to abandon his nuclear program, which remains intact, according to a recent confidential UN report.

Pompeo told Tapper that Trump is focused on getting "a demonstrable, verifiable" step toward denuclearization during the summit.

"There are many things he could do to demonstrate his commitment to denuclearization," Pompeo said.

The secretary of state also said that core sanctions from the U.N. Security Council resolution on North Korea will be removed only after it fully denuclearizes, telling Tapper that the administration's standard for removing sanctions has always been "full, verified denuclearization."

A senior administration official told CNN last week that they're not sure if the country has made the decision to denuclearize, "but the reason why we're engaged in this is because we believe there's a possibility that North Korea can make the choice to fully denuclearize."

"And that's why the President has assigned such a priority to engaging with them," the official added.