SEOUL, South Korea -- South Korean President Moon Jae-in on Wednesday downplayed concerns that the resumption of inter-Korean dialogue will be accompanied by an easing of international sanctions and pressure on North Korea over its nuclear program.

Moon made the comments in a meeting with political party leaders a day after South Korea announced an agreement with the North to hold a rare summit in April. Senior South Korean officials who met with North Korean leader Kim Jong Un in Pyongyang on Monday also said the North expressed a willingness to hold talks with the United States on denuclearization and normalizing ties.

Conservative opposition leaders expressed concern during Wednesday's meeting at Seoul's presidential palace that North Korea could use the talks as a way to reduce the pressure, and also questioned whether the North in genuinely interested in abandoning its nuclear weapons.

"The sanctions and pressure on North Korea aren't maintained by South Korea alone - these are actions based on U.N. Security Council resolutions, and then there are strong unilateral sanctions imposed by the United States," Moon said, added that the pressure on the North could only be reduced by "substantive progress" on denuclearization.

Get Breaking News Delivered to Your Inbox

"These international efforts (to pressure the North) cannot be loosened by inter-Korean dialogue. We don't aim for that to happen and it's also impossible."

Moon's presidential national security director, Chung Eui-yong, who led the South Korean delegation that met with Kim, is to leave for the United States on Thursday to brief U.S. officials on the outcome of his trip to the North. Chung told reporters on Tuesday that he received a message from North Korea intended for the United States, but didn't disclose what it was.

The fact that the North wants to talk at all is almost certainly due to economic sanctions biting the regime hard. The U.S. is keeping up its so-called maximum pressure strategy against North Korea, announcing new sanctions on Monday, CBS News correspondent Holly Williams reports.

Japan has responded cautiously to the South Korean announcement of summit talks, saying Tokyo's policy of keeping maximum pressure on North Korea is unchanged.

South Korean President Moon Jae-in talks with Kim Yo Jong, the sister of North Korea's leader Kim Jong Un, after watching North Korea's Samjiyon Orchestra's performance in Seoul, South Korea, February 11, 2018. REUTERS

Chief Cabinet Secretary Yoshihide Suga said Wednesday that dialogue for dialogue's sake is meaningless and that the allies "should fully take into consideration lessons from our past dialogues with the North, none of which achieved denuclearization." He said Japan is on the same page as the United States, citing U.S. Vice President Mike Pence as saying Washington's pressure campaign is unchanged, with all options still on the table.China, which is North Korea's only major ally, cheered the exchanges between the Koreas and called for a return to six-nation talks on denuclearization that it previously hosted.

Foreign ministry spokesman Geng Shuang told reporters Wednesday that China was "pleased to see the positive outcomes from those exchanges and interactions between the two sides. ... We hope the North and South will earnestly implement their consensuses and proceed with the process of reconciliation and cooperation."