Moon Jae-in spoke before two senior Seoul officials left for the United States to brief officials about the outcome of their recent visit to North Korea.
The Seoul officials said North Korea offered talks with the United States over normalising ties and denuclearization of the Korean Peninsula. Seoul said the North also agreed to suspend nuclear and missile tests during such future talks.
Some experts question how sincere North Korea is about its reported offers, citing what they call its track record of using past disarmament talks to wrest aid and concessions while covertly continuing its bomb programme.
That's the same position North Korea has long maintained to justify its nuclear programme or call for the withdrawal of 28,500 US troops and a halt to annual US-South Korean military drills as a condition for scrapping its nuclear programme. The North sees the allies' drills as an invasion rehearsal.
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Choi Hyunsoo, spokeswoman of Seoul's Defence Ministry, said the military will announce the schedule for the joint drills after the Pyeongchang Paralympics, which start Friday and run through March 18.
Moon still described the outcome of his envoys' North Korea trip "a big step toward denuclearization of the Korean Peninsula" that was possible with "a strong support" by the US government.
It's unclear whether the United States would accept the North's reported offer for talks. President Donald Trump expressed both hope and skepticism, calling the North's move "possible progress" that also "may be false hope."
The North responded to past joint drills by the allies with its own weapons tests and fiery rhetoric.
Japanese Prime Minister Shinzo Abe said Japan's policy of pressuring North Korea does not change just because its leadership is now open to dialogue.
"We should not ease our stance, for instance relax sanctions, just because North Korea agreed to have a dialogue," Abe told a parliamentary session. "We should not give North Korea a reward in exchange for a dialogue."
"This proves that China's proposal of suspension for suspension was the right prescription for the problem and created basic conditions for the improvement of inter-Korean relations," Foreign Minister Wang Yi told reporters in Beijing. Wang said Pyongyang's security concerns should be addressed in return for denuclearization.
Moon and North Korean leader Kim Jong Un are to meet at a border village in late April, when the South Korea-US drills would likely be still under way. If realized, the Moon-Kim meeting would mark the rivals' third-ever summit talks since their 1945 division, according to Moon's office.