President Donald Trump said after North Korea's latest failed rocket launch that communist leader Kim Jong-Un will eventually develop better missiles, and "we can't allow it to happen."
In a taped interview broadcast Sunday on CBS' "Face the Nation," the president would not discuss the possibility of military action, saying: "It is a chess game. I just don't want people to know what my thinking is."
Separately, Trump's national security adviser, Army Lt. Gen. H.R. McMaster, said North Korea's most recent missile test represents "open defiance of the international community." He said North Korea poses "a grave threat," not just to the U.S. and its Asian allies, but also to China.
Speaking on "Fox News Sunday," McMaster said it is important "for all of us to confront this regime, this regime that is pursuing the weaponization of a missile with a nuclear weapon."
"This is something that we know we cannot tolerate," McMaster said.
On Saturday, a North Korean mid-range ballistic missile broke up a few minutes after launch, the third test-fire flop this month. The program's repeated failures over the past few years have given rise to suspicions of U.S. sabotage.
In the CBS interview, the president was asked why the North's rockets keep blowing up.
"I'd rather not discuss it," he said. "But perhaps they're just not very good missiles. But eventually, he'll have good missiles."
He added: "And if that happens, we can't allow it to happen."
Trump also called North Korea's leader "a pretty smart cookie" for being able to hold onto power after taking over at a young age. "People are saying, 'Is he sane?' I have no idea," the president said.
North Korean ballistic missile tests are banned by the United Nations because they are seen as part of the North's push for a nuclear-tipped weapon that can hit the U.S. mainland.
McMaster said that Trump "has made clear that he is going to resolve this issue one way or the other," but that the president's preference is to work with China and others to resolve it without military action.
That means, McMaster said, working to enforce current U.N. sanctions and perhaps ratcheting them up. "And it also means being prepared for military operations if necessary," he said.
Trump said he believes China's president, Xi Jinping, has been putting pressure on North Korea over its missile and nuclear weapons programs.
The launch comes at a point of particularly high tension in the region. Trump has sent a nuclear-powered submarine and an aircraft carrier to Korean waters.
The U.S. and South Korea also started installing a missile defense system that is supposed to be partially operational within days.
Residents in the village of Seongj, where the missile defense system is being installed, scuffled with police on Sunday. About 300 protesters faced off against 800 police and succeeded in blocking two U.S. Army oil trucks from entering the site, local media reported. A few residents were injured or fainted from the scuffle and were taken to a hospital.
The Terminal High-Altitude Area Defense system, or THAAD, is controversial in South Korea, and presidential front-runner Moon Jae-in has vowed to reconsider the deployment if he wins the May 9 election.
He has said that the security benefits of THAAD would be offset by worsened relations with China, which is the country's biggest trading partner and is opposed to its deployment.
Trump raised eyebrows in South Korea last week when he said would make Seoul pay $1 billion for the missile defense system. McMaster said Sunday that the matter is subject to negotiation.