UNITED NATIONS — Three days after offering to talk to North Korea “without precondition,” Secretary of State Rex W. Tillerson reversed course, insisting — as President Trump has all along — that the North must stop its nuclear threats and “earn its way” to negotiations.

“A sustained cessation of North Korea’s threatening behaviour must occur before talks can begin,” Mr Tillerson said at a United Nations Security Council meeting.

His remarks on Friday (Dec 15) were a sharp contrast from his surprisingly conciliatory comments, made Tuesday, in which he said he was open to talking to the North about anything, including, as he put it, “the weather.” The White House swiftly distanced itself, saying that talks would be pointless so long as the North continued to threaten its neighbours and the United States.

On Friday, Mr Tillerson reiterated Mr Trump’s position. “North Korea must earn its way back to the table,” Mr Tillerson said. “The pressure campaign must and will continue until denuclearization is achieved.”

The back and forth reflected the awkward gulf between Mr Tillerson and Mr Trump, who has threatened to “totally destroy” the country and referred to its leader, Kim Jong-un, as “little rocket man.”

Mr Tillerson’s latest message also appeared to place the United States and North Korea at a dangerous standoff once more, with Washington insisting on a halt to the North’s nuclear weapons and ballistic missile programs and North Korea advancing them.

The United Nations secretary general, Mr António Guterres, called the North Korean nuclear crisis the world’s “most tense and dangerous security issue,” and without identifying the United States by name, warned of the risk of bellicose language. He said it was imperative to open lines of communication.

“While all concerned seek to avoid an accidental escalation leading to conflict, the risk is being multiplied by misplaced overconfidence, dangerous narratives and rhetoric, and the lack of communication channels,” he said.

One of his top aides, Mr Jeffrey D. Feltman, under secretary general for political affairs, met with senior government officials in Pyongyang, the North’s capital, earlier this month, the first high level visit by a United Nations official since 2011. Mr Feltman, a diplomat, said he did not receive any commitments from the North, but “left the door ajar” for a negotiated settlement. The United Nations has suggested holding talks to figure out the substance of negotiations further down the line, and a military-to-military hotline to dampen risks of conflict.

China sounded more like a marriage counsellor in the Security Council chamber, warning against “mutual blaming.”

“The parties concerned should keep calm and exercise restraint,” China’s deputy permanent representative, Mr Wu Haitao, said.

The North Korean ambassador to the United Nations, Mr Ja Song-nam, in a rare appearance in the Council, began by condemning Japan for hosting the session and went on to criticise the Council for acting as “a tool” of the United States.

The Council meeting came weeks after the North fired an intercontinental ballistic missile that flew higher and longer than previous such launches and that the North claimed could deliver heavy nuclear warheads anywhere in the continental United States. It has conducted six nuclear tests so far.

Since late 2016, the Council has imposed a series of sanctions aimed at cutting the North’s ability to fund its nuclear weapons program, including limiting its ability to export labourers for work programs in Russia and other countries.

Mr Tillerson on Friday used the Security Council session to scold Russia for employing North Korean workers in what he called “slave-like” conditions and which he said “calls into question Russia’s dedication as a partner for peace.”

The Security Council meeting came a day after President Vladimir V. Putin of Russia praised Mr Trump’s achievements in his first year in office, and Mr Trump called on the Kremlin to help with the North Korean crisis.

Russia’s United Nations ambassador, Mr Vassily A. Nebenzia, rebuffed Mr Tillerson’s criticism of his country’s labour imports from North Korea and questioned the United States’ “sincerity” in defusing tensions on the Korean Peninsula. Russia and China have criticized the American military exercises conducted with South Korean forces.

Asked after the meeting about what he had meant with his offer of talks “without precondition” earlier in the week, Mr Tillerson said the United States would not accept preconditions imposed by others, such as a proposal by Russia and China to freeze nuclear tests in exchange for a freeze on the American military exercises on the Korean Peninsula. Mr Tillerson also said the United States would not ease sanctions before any possible talks.

“We are not going to accept preconditions for these talks,” he said. “But as I indicated in my remarks our communication channels remain open. North Korea knows they’re open. They know where the door is. They know where to walk through that door when they want to talk.”

Ms Heather Nauert, the State Department spokeswoman, said that Mr Tillerson “wants to keep channels of communication open for the purposes of testing the effects of sanctions and to avoid miscalculation.”

“These are not negotiations,” Ms Nauert added, “and there will be no change in the international pressure campaign connected with this.”

President Trump has made no secret of his disagreements with Mr Tillerson over North Korea.

In October, Mr Trump tweeted that Mr Tillerson was “wasting his time” trying to open diplomatic lines to North Korea.

The latest back-and-forth followed reports that the White House was laying the groundwork for the secretary’s departure from the State Department and his replacement by Mr Mike Pompeo, the C.I.A. director. THE NEW YORK TIMES