President Moon Jae-in called Tuesday for watertight national security and vowed to fulfill his duty as commander-in-chief until his term ends, a day after his office voiced concern successor-elect Yoon Suk-yeol's plan to relocate the presidential office could leave a security vacuum.

Moon, whose term ends on May 9, said during a Cabinet meeting that his "last mission" is to "fulfill duties as head of state, chief of the administration, and commander-in-chief of the military that the Constitution has granted to the president."

Moon also said the security situation on the Korean Peninsula is "grave."

"It is time for our military to maintain its highest security readiness," Moon said.

Moon's remarks were seen as thinly veiled opposition to Yoon's plan to relocate the presidential office out of Cheong Wa Dae before his inauguration on May 10.

On Sunday, Yoon officially announced his decision to move the presidential office to what is now the defense ministry building, saying he wants the top office to move out of a "symbol of imperial power" and get closer to the people.

But the relocation push has hit a snag as Moon's office expressed opposition, saying such a hurried relocation could cause a security vacuum and confusion at a time of rising tensions on the Korean Peninsula.

"There should be no small factor of anxiety in security," Moon said. "We need to be more vigilant during the change of government and make every effort for stable management of the situation on the Korean Peninsula."

Meanwhile, Moon said South Korea has moved past the peak of the omicron variant, but the number of critically ill patients and deaths are expected to rise.

Moon urged government ministries to make all-out efforts to minimize COVID-19 deaths and stabilize medical response, including the bed occupancy rate. (Yonhap)