The White House has ruled out a dialogue with North Korea until it “fundamentally improves its behaviour”, once again contradicting the secretary of state Rex Tillerson, who said on Tuesday the US was ready to begin direct talks without preconditions.

A statement given to Reuters by the National Security Council spokesman, saying “clearly right now is not the time” for talks, following North Korea’s test launch of a intercontinental ballistic missile last month.

The statement seemed to close the door on a diplomatic window only hours after it had been opened by the administration’s top diplomat.

The mixed messages underlined the chaotic nature of Trump administration foreign policy, and raised new questions over how long Tillerson can stay in the administration that has persistently undercut him.

On Tuesday, Tillerson told an audience of foreign policy experts in Washington: “We’ve said from the diplomatic side we’re ready to talk any time North Korea, would like to talk, and we’re ready to have the first meeting without precondition.”

In the most direct overture to Pyongyang to date, the secretary of state said: “Let’s just meet, and we can talk about the weather if you want. We can talk about whether it’s going to be a square table or a round table, if that’s what you’re excited about. But can we at least sit down and see each other face to face?”

The one condition Tillerson laid down was that there had to be a pause in North Korean nuclear and missile tests, but he presented that as a practical consideration rather than a demand for a concession from Pyongyang on a matter of principle.

The tone of Tillerson’s comments marked a clear break from the state department formula before Tuesday that North Korea would have to show it was “serious about denuclearization” before contact could start. US officials had said that meant North Korea would have to commit to putting its nuclear weapons programme on the table in any eventual substantive negotiations.

The state department spokeswoman, Heather Nauert insisted on Wednesday “the secretary is on the same page as the White House” and said repeatedly that “the policy has not changed”. However, it was not clear how Tillerson’s presentation on Tuesday was compatible with either the White House statement or previous state department descriptions of policy.

Adding to confusion, Nauert appeared to reintroduce the precondition that Pyongyang had to be ready eventually to disarm.

“We remain open to dialogue when North Korea is willing to conduct a credible dialogue on the peaceful denuclearization of the Korean peninsula,” she said. “We are not seeing any evidence that they are ready to sit down and have those kind of conversations right now.”

Tillerson’s remarks followed a trip to Pyongyang by the UN’s under-secretary general for political affairs, Jeffrey Feltman, a former US diplomat. During the visit, the first by such a high-ranking UN official for six years, Feltman met the foreign minister Ri Yong-ho, and warned that “time is of the essence” in establishing a dialogue.

Feltman also noted “the urgent need to prevent miscalculations and open channels to reduce the risks of conflict”, an apparent reference to a proposal to set up a military-to-military channel as a first step in resuming a dialogue, and lessening the risk of an accidental encounter between the two sides escalating into full-scale war.

Suzanne DiMaggio, a senior director at the New America thinktank and a leading participant in back-channel contacts with North Korea, said that both sides felt they were in a position of strength, after North Korea’s successful tests of a powerful intercontinental ballistic missile in November and an apparent hydrogen bomb in September, while the US had marshaled a global consensus behind new economic pressure on Pyongyang.

Commenting on Tillerson’s statement, DiMaggio said: “It looks like there is recognition inside the administration that a big effort is needed to avoid a catastrophic confrontation.”

But she warned that for the opportunity for dialogue not to be lost, “it’s more important than ever that the administration speak with one voice”.

Commenting on the mixed messages, Vipin Narang, an expert on the North Korean nuclear programme at the Massachusetts Institute of Technology, tweeted: “Ambiguity can enhance deterrence, confusion can kill it. This is confusion.”

This is not the first time the White House has contradicted Rex Tillerson on policy towards North Korea. In early October, when Tillerson was visiting China and raised the possibility of contacts with North Korea, Trump tweeted that he had told his secretary of state to “save his energy”.

At the end of November, Tillerson had to fight off anonymous briefings from the White House that he was about to be fired and replaced by the CIA director, Mike Pompeo.

In laying out the case for talks on Tuesday, Tillerson said that an initial dialogue would serve to learn more about Kim.

“We’re dealing with a new leader in North Korea that no one’s ever engaged with,” he said at a meeting organised by the Atlantic Council thinktank. “And he clearly is not like his father, nor is he like his grandfather, and we don’t know a whole lot about what it will be like to engage with him. I have to know who my counterpart is. I have to know something about them.”

Kim has staked his credibility within the regime on the success of the nuclear weapons programme, and congratulated his country’s scientists on Tuesday who he said had “successfully carried out the great historic cause of completing the state nuclear force”, echoing the language of an earlier official statement suggesting the regime believes it has achieved its aim of developing the capacity to carry out a nuclear strike on the US mainland.

But the North Korean dictator said scientists and workers would continue manufacturing “more latest weapons and equipment” to “bolster up the nuclear force in quality and quantity”, according to the state news agency.