FILE PHOTO - A North Korean flag flies on a mast at the Permanent Mission of North Korea in Geneva October 2, 2014. REUTERS/Denis Balibouse/File Photo

WASHINGTON (Reuters) - No negotiations can be held with North Korea until it improves its behaviour, a White House official said on Wednesday, raising questions about U.S. Secretary of State Rex Tillerson’s offer to begin talks with Pyongyang anytime and without pre-conditions.

“Given North Korea’s most recent missile test, clearly right now is not the time (for negotiations),” the White House National Security Council spokesman told Reuters.

Tillerson said on Tuesday the United States was “ready to talk anytime North Korea would like to talk,” backing away from a key U.S. demand that Pyongyang must first accept that any negotiations would have to be about giving up its nuclear arsenal.

The White House has declined to say whether President Donald Trump, who has taken a tougher rhetorical line with North Korea than his chief diplomat, gave approval for the diplomatic overture.

A day after Tillerson’s appearance before Washington’s Atlantic Council think tank, the White House official, who declined to be named, laid out a different formula for any engagement with North Korea.

“The administration is united in insisting that any negotiations with North Korea must wait until the regime fundamentally improves its behaviour,” the official said. “As the secretary of state himself has said, this must include, but is not limited to, no further nuclear or missile tests.”

In his speech, however, Tillerson did not explicitly set a testing freeze as a requirement before talks can begin. He said it would be “tough to talk” if Pyongyang decided to test another device in the middle of discussions and that “a period of quiet” would be needed for productive discussions.

The apparent shift in Tillerson’s thinking came nearly two weeks after North Korea said it had successfully tested a breakthrough intercontinental ballistic missile (ICBM) that put the entire United States mainland within range.

North Korea has made clear it has little interest in negotiations with the United States until it has developed the ability to hit the U.S. mainland with a nuclear-tipped missile, something most experts say it has still not proved.