Donald Trump enlisted Friday the help of China's Xi Jinping to keep sanctions pressure on North Korea, amid fears that an audacious diplomatic gambit by the US president could lead to backsliding.
In an evening tweet, Trump praised a possible future agreement with the communist North as "very good" for the international community as a whole, after the US leader stunned the world by accepting an invitation to meet Kim Jong Un before the end of May.
"The deal with North Korea is very much in the making and will be, if completed, a very good one for the World. Time and place to be determined," Trump wrote.
During a telephone conversation, Trump and the ever-more-powerful Chinese president committed to "maintain pressure and sanctions until North Korea takes tangible steps toward complete, verifiable, and irreversible denuclearization," according to the White House.
As aides scrambled to catch up with Trump's decision -- taken before consulting key confidantes -- the White House sent mixed messages about conditions.
"They've made promises to denuclearise, they've made promises to stop nuclear and missile testing," White House spokeswoman Sarah Sanders said.
"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," she told reporters.
A day after the bombshell announcement that the US and North Korean leaders would meet, Vice President Mike Pence said the White House would keep "maximum pressure" on Pyongyang and claimed US efforts to isolate Kim had been vindicated.
There has been limited reaction from Kim's regime, but South Korean President Moon Jae-in said news of the summit -- announced by his national security advisor on a visit to Washington -- was "like a miracle."
For his part, Xi urged the two leaders to begin talks as "soon as possible" and praised Trump's "positive aspiration."
The UN Security Council has imposed tough economic sanctions aimed at choking off revenue to Pyongyang's military programs after Kim's regime carried out a sixth nuclear test and advanced missile launches.
German Chancellor Angela Merkel was among the world leaders to hail the announcement as a "glimmer of hope," saying North Korea's nuclear drive "has been a source of great concern for all of us."
The International Atomic Energy Agency, the UN's nuclear watchdog, voiced hope the summit would produce "concrete progress" and a resumption of long-suspended nuclear inspections.