Trump made the remark while he met with Moon Jae-in, South Korea's president, for pivotal discussions ahead of the American president's planned meeting with the North Korean dictator.
"Whether or not it happens, you'll be knowing pretty soon," Trump told reporters at the White House. He also declined to say whether he has spoken with North Korea's leader.
The summit is scheduled for June 12 in Singapore, which is widely viewed as a neutral site. Yet doubts continue to grow about whether the meeting will actually take place. Trump's remarks Tuesday were the strongest indication yet that the summit might not happen as planned.
Last week, North Korea said it would reconsider whether to hold the meeting after abruptly canceling talks with South Korea amid joint military drills with the U.S. on the Korean Peninsula.
The communist dictatorship also took issue with Trump's national security advisor, John Bolton, who suggested using a denuclearization model similar to one used with North African country Libya. The nation's dictator at the time, Moammar Gadhafi, agreed to give up nuclear weapons in exchange for relaxed U.S. sanctions. Eventually, however, the U.S. supported a violent overthrow of Gadhafi.
North Korea called any attempt to impose a Libya-style arrangement on the country "awfully sinister." Trump has said, though, that the "Libyan model isn't a model that we have at all."