WASHINGTON — America’s top diplomat stepped back Friday from his offer of unconditional talks with North Korea, telling world powers the nuclear-armed nation must earn the right to negotiate with the United States.

Secretary of State Rex Tillerson’s declaration before the U.N. Security Council marked a stunning reversal after he proposed discussions with Pyongyang without preconditions earlier this week. That overture was almost immediately rebutted by White House officials.

Still, Mr. Tillerson had planned to reiterate his call at a special U.N. ministerial meeting on North Korea at the council Friday morning. His prepared remarks suggested only that North Korea would have to undertake a sustained halt in its threatening behavior before talks could begin. But Mr. Tillerson changed the script.

“North Korea must earn its way back to the table,” Mr. Tillerson told the foreign ministers. “The pressure campaign must and will continue until denuclearization is achieved. We will in the meantime keep our channels of communication open.”

The debate over offering North Korea unconditional talks reflects the differences within the Trump administration as it runs out of time to prevent North Korea from perfecting a nuclear-tipped missile that can strike the U.S. mainland. President Donald Trump has vowed to prevent such capability, with military action if necessary.

Defense Secretary Jim Mattis on Friday said North Korea’s most recent test of a long-range missile did not demonstrate an imminent threat to the United States.

Shortly after the late-November test, Mr. Mattis said the missile flew higher than any previous North Korean test, and that it represented a continued effort to build a missile capable of threatening the U.S.

In an exchange with reporters at the Pentagon on Friday, Mr. Mattis was asked whether the missile test indicated an imminent threat of nuclear attack on the U.S.

His response was: “No, not yet.” He said U.S. experts are still doing what he called “forensic analysis.” This presumably refers to studies of imagery of the missile in flight and the re-entry of its mock warhead into the Earth’s atmosphere.

So far, U.S.-led sanctions on North Korea and diplomatic isolation haven’t compelled Kim Jong Un’s government to stop its nuclear and missile tests, or to seek negotiations.

Asked Friday if he supported unconditional talks, Mr. Trump did not answer directly.

“Well, we’re going to see what happens with North Korea. We have a lot of support. There are a lot of nations that agree with us — almost everybody,” Mr. Trump told reporters. He credited China — which accounts for about 90 percent of North Korea’s external trade — with helping on pressuring North Korea, while Russia was not.

“We’d like to have Russia’s help — very important,” said Mr. Trump. He raised it in a Thursday phone call with Russian President Vladimir Putin.

Mr. Tillerson and Mr. Trump have appeared to clash before on North Korea, amid questions about the former ExxonMobil executive’s future as top diplomat. In October, Mr. Trump said Mr. Tillerson was “wasting his time” trying to negotiate with the North.

First Published: December 16, 2017, 4:26 a.m.