WASHINGTON >> America’s top diplomat stepped back today 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, 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 Tillerson changed the script.

“North Korea must earn its way back to the table,” 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.

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, 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,” 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 Trump. He raised it in a Thursday phone call with Russian President Vladimir Putin.

At the U.N. Tillerson called on China and Russia to go beyond U.N.-mandated economic sanctions. He said North Korean laborers were toiling in “slave-like conditions” in Russia for wages used to fund nuclear weapons, while China was still allowing crude oil to flow into North Korean refineries.

North Korea has conducted more than 20 ballistic missile tests during 2017 and its most powerful nuclear explosion to date. Its more recent missile test in late November fired a projectile that experts say could carry a nuclear warhead to the U.S. Eastern Seaboard.

Tillerson said the North’s growing capabilities were a “direct threat to our security and the security of the entire world. We do not regard this claim as an empty threat.”

He said U.S. does not want war, but “will use all necessary measures to defend itself against North Korean aggression.” He said “our hope remains that diplomacy will produce a resolution.”