US President Donald Trump has sounded a note of caution about his much-vaunted summit with Kim Jong Un, saying "well see" after Pyongyang threatened to cancel plans for the June 12 meeting in Singapore. South Korea said on Thursday it would seek to mediate between the US and North Korea. "We havent been notified at all. Well have to see," Trump said about the North Korean threat. "We havent seen anything. We havent heard anything. We will see what happens. Whatever it is, it is."  After weeks of warm words and diplomatic backslapping, Pyongyang abruptly threatened to pull out Tuesday, over US demands for "unilateral nuclear abandonment." In an angrily worded statement, the North warned "if the US is trying to drive us into a corner to force our unilateral nuclear abandonment, we will no longer be interested in such dialogue." In that case, Pyongyang would have to "reconsider" its participation at next months summit in Singapore, it said. Washington is pressing for North Koreas complete, verifiable and irreversible denuclearization. But so far, the North has given no public indication of what it is offering, beyond a broad commitment to denuclearization of the "Korean peninsula." China, North Koreas sole major ally, called for the summit to go ahead. "The situation on the peninsula has eased up, which is worth cherishing," Chinese foreign ministry spokesman Lu Kang told a regular briefing.  French Foreign Minister Jean-Yves Le Drian urged North Korea to "demonstrate its sincerity to negotiate on its denuclearization." During a meeting with his Chinese counterpart Wang Yi, Le Drian said: "Highs and lows can come along as the recent news from the peninsula shows, but we must not lose sight of the goal." The White House said plans for the summit were moving ahead. "The president is ready if the meeting takes place. And if it doesnt, we will continue the maximum pressure campaign that has been ongoing," White House Press Secretary Sarah Sanders said. The North Korean warning follows a weeks-long charm offensive that has seen Kim Jong Un hold a historic summit with the Souths president and meet twice with Chinese President Xi Jinping. Pyongyang had raised hopes ahead of the US summit by announcing it will destroy its nuclear testing site next week. South Koreas presidential Blue House also said it would seek to bridge the gap betweenWashington and Pyongyang. A Blue House official said the South Korean government or President Moon Jae-in intends to more actively perform "the role of a mediator" between South Korea, the US and North Korea. Trump will host Moon at a summit at the White House on May 22, and the two are expected to discuss the upcoming US-North Korea summit.