Trump, who has grappled with nuclear tests and ballistic missile launches by North Korea since he took office a year ago, said Pyongyang is steadily advancing in its ability to deliver a missile to the United States.

“They’re not there yet, but they’re close. And they get closer every day,” said Trump.

North Korea said after its last intercontinental ballistic missile launch in November that the test had put the U.S. mainland within range. Some experts agreed that based on the missile’s trajectory and distance it had the capability to fly as far as Washington D.C.

They said, however, that North Korea had not yet offered any proof that it had mastered all technical hurdles, including development of a re-entry vehicle needed to deliver a heavy nuclear warhead reliably atop an ICBM, but it was likely that it soon would. Pyongyang could reach that milestone by the end of the year, some intelligence officials said.

He would not say whether the United States has been considering a limited, pre-emptive attack to show the North that the United States means business.

“We’re playing a very, very hard game of poker and you don’t want to reveal your hand,” he said.