The White House on Friday sent confusing messages about the prospects for a historic meeting between President Trump and North Korean leader Kim Jong Un, raising questions about a summit announced less than 24 hours earlier.

White House officials insisted that nothing had changed since Trump said he had accepted an invitation from Kim. But White House press secretary Sarah Huckabee Sanders appeared to lay out new conditions, demanding “concrete, verifiable” actions from Pyongyang.

She repeated the demand several times, saying: “They’ve got to follow through on the promises that they’ve made, and we want to see concrete and verifiable actions. The president has accepted that invitation on the basis that we see concrete and verifiable steps.”

The remarks left it unclear whether the White House was restating the terms of the meeting, with even the timing of talks appearing to be up in the air.

President Trump agreed March 8 to meet with North Korean leader Kim Jong Un "by May." Here are three other big events in North Korean diplomacy. (Jason Aldag/The Washington Post)

The White House insistence on concrete actions appeared to be a response to criticism that Trump accepted Kim’s invitation too quickly, without extracting enough concessions beforehand. 

With most big international treaties, the leaders of the countries involved swoop in at the end to cap a diplomatic success. But that well-worn script is being upended, despite negotiations that would be inherently more complicated than two previous initiatives to get North Korea to give up its nuclear weapons program in exchange for aid — largely because North Korea now has an arsenal of nuclear weapons in hand.

While far from complete, plans are starting to be cobbled together to establish the parameters of future talks.

A senior State Department official said the planned talks between Trump and Kim would amount to just that: talks. Subsequently, if the conditions were ripe, they would evolve into formal negotiations, the official said.

“Negotiations then are a process of writing down on paper what both sides are willing to do, what the commitments are, how those commitments are going to be fulfilled, how they’re going to be verified, and who gets what for making those commitments, then actually fulfilling those commitments,” the official said. “That’s what a negotiation is.”

The White House and the State Department both say the United States will continue exerting a “maximum pressure” campaign of strict sanctions.

If talks blossomed into negotiations, it would mark the third time the United States and North Korea engaged in a full-fledged diplomatic push to denuclearize the Korean Peninsula.

In 1994, the two countries signed an agreement in which Pyongyang committed to freezing a plutonium weapons program in exchange for aid. But it collapsed in 2002.

The George W. Bush administration made a breakthrough in 2007 when Pyongyang promised to begin dismantling its nuclear program during six-party talks that also included South Korea, China, Russia and Japan. But those discussions imploded in 2009 after North Korea launched a satellite.

In both cases, the Clinton and Bush administrations first tested the waters with talks involving lower-level officials. Trump is now flipping the script with a meeting of leaders at the outset — a riskier proposition.

On Friday, Trump won cautious support from Republicans in Congress with his bold gambit, but analysts warned that the tide could shift quickly. 

Christopher R. Hill, a former ambassador under Bush, faced withering attacks from neoconservatives for engaging with Pyongyang during the six-party talks that began in 2005. 

“People like John Bolton said I was a traitor for talking to the North Koreans,” Hill said in an interview, referring to the former U.S. ambassador to the United Nations. 

Hill, who met with a group of Republican lawmakers Wednesday, including Rep. Steve King (Iowa), said conservatives now appear more tolerant of talks, at least initially, than during the Bush era.

“I must say I was struck by how they want to see a solution to this,” he said. “There’s a difference in this group than the neoconservatives, where the mere act of meeting with the Koreans was considered an act of disloyalty.” 

Bolton, for his part, offered conditioned praise for Trump, saying Friday that he expected the president to deliver a warning about U.S. willingness to use military force. 

If the Trump-Kim meeting is held in May, it would coincide with a deadline for another nuclear deal, the one forged by the Obama administration with Iran and other world powers in 2015. Trump has called it the worst deal ever negotiated. Though international monitors have said Iran is abiding by its commitments, Trump has threatened to reimpose nuclear-related sanctions and withdraw from it in May under a congressional mandate.

Talks with North Korea could breathe new life into that deal.

“If logic prevails, this could make it less likely that Donald Trump unilaterally blows up the Iran nuclear deal, which is working,” said Daryl Kimball, executive director of the Arms Control Association.

Kimball believes that negotiations could succeed with ­confidence-building measures: North Korea maintains a halt in its nuclear and missile testing, for example, and the United States modifies joint military exercises with South Korea so that U.S. bombers do not approach North Korean territory.  

“What I’d say to those who are skeptical and argue we can’t trust the North Koreans, well, I’m skeptical, too,” Kimball said. “I don’t trust the North Koreans. But we have to test this option. It’s a hell of a lot better than allowing them to continue with their nuclear program or having a catastrophic war.”

Wendy Sherman, who was the North Korea policy coordinator during the Clinton administration and the lead negotiator with Iran for the nuclear deal, cautioned that an enduring relationship would depend on whether the two sides had the same expectations.

“The mismatch of expectations led to some of the problems in the past,” she said. “They thought they were getting the normalization of relations with the United States, which never happened, and we thought we were stopping their ability to stock fissile material.”

Negotiations now are bound to be more difficult than previous rounds, and North Korea has more leverage than it did before.

“Everything we’ve learned is useful but not adequate, because at no other time did North Korea have nuclear weapons and the means to deliver them,” Sherman said. “We’re at a different place with different challenges.”