President Trump will insist on “concrete, verifiable actions” from North Korea before holding a promised summit with North Korean leader Kim Jong Un, the White House said Friday, adding conditions and a note of skepticism to the buoyant mood that surrounded the surprise announcement the night before.

Press secretary Sarah Huckabee Sanders repeated the insistence on “concrete, verifiable” steps several times, and asserted that the United States had given up no leverage in agreeing to hold the unprecedented meeting.

“They've got to follow through on the promises that they’ve made, and we want to see concrete and verifiable actions,” Sanders said. “The president has accepted that invitation on the basis that we see concrete and verifiable steps.”

She was vague about exactly what that meant, and whether the United States would scrap the meeting if North Korea does not take actions toward getting rid of its nuclear weapons.

U.S. and South Korean officials had previously said that in extending the offer to meet, North Korea had pledged to refrain from nuclear and ballistic missile testing. North Korea had also said talks would be about denuclearization, but it is not clear that Pyongyang agreed to do anything toward that end before a meeting that South Korea said would take place “by May.”

Trump’s agreement gave North Korea one thing it has wanted for decades: Public parity for its leader and the president of the United States.

Sanders insisted that Trump had given up nothing.

“The president is hopeful that we can make some continued progress. Look, what we know is that the maximum-pressure campaign has clearly been effective. We know that it has put a tremendous amount of pressure on North Korea,” she said, referring to the tough sanctions and rhetoric the White House has applied over the last year.

“And they have made some major promises. They’ve made promises to denuclearize. They’ve made promises to stop nuclear and missile testing. And they’ve recognized that regular military exercises between the U.S. and its ally, South Korea, will continue,” Sanders said. “We’re not letting up. We’re not going to step back or make any changes to that. We’re going to continue in that effort. And we’re not going to have this meeting take place until we see concrete actions that match the words and the rhetoric of North Korea.”