SEOUL, May 27 (Reuters) - North Korean leader Kim Jong Un reaffirmed his commitment to "complete" denuclearisation of the Korean peninsula and to a planned meeting with U.S. President Donald Trump, South Korean President Moon Jae-in said on Sunday.

Moon and Kim agreed at a surprise second meeting on Saturday that a possible North Korea-U.S. summit, currently planned for June 12 in Singapore, must be held successfully, Moon told a news conference in Seoul.

Moon, who returned to Seoul on Thursday morning after meeting Trump in Washington in a bid to keep the high-stakes U.S.-North Korea summit on track, said he delivered Trump's "firm will" to end the hostile relationship with North Korea and pursue bilateral economic cooperation. (Reporting by Soyoung Kim and Hyonhee Shin in SEOUL Editing by Paul Tait)