South Korean national security adviser Chung Eui-yong on Monday said he believes there is a “99.9 percent chance” a planned North Korea-U.S. summit will take place.

Speaking on board South Korea’s Air Force One en route to Washington DC, Chief of the National Security Office (NSO) Chung said South Korean President Moon Jae-in and U.S. President Donald Trump were set to discuss next month’s summit in meetings on Tuesday.

“Above all, the summit on June 12 in Singapore must take place. If it happens, we expect that the agreement will be reached in the direction that we hope,” he told