South Korea's biggest opposition party said Thursday that next week's summit between the United States and North Korea should be called off unless Pyongyang agrees to fully denuclearize.

"The most important thing is that CVID (complete, verifiable and irreversible denuclearization) must be achieved through next week's U.S.-North Korea summit, and if the North goes against it, it is rather reasonable to cancel the meeting right away," Liberty Korea Party Chairman Hong Joon Pyo told a press conference in Seoul.

(Hong Joon Pyo, center, campaigns in Seoul on May 31 for local elections)

The United States and its allies like South Korea are calling for a process that would require North Korea to abandon its nuclear arsenal and its weapons-building infrastructure and development programs, while also submitting to international inspections and monitoring to ensure the shift would be complete and permanent.

Hong also opposed declaring an official end to the 1950-1953 Korean War, which ended with an armistice, on the occasion of next Tuesday's summit in Singapore, suggesting that such a move should only come after thoroughly discussing denuclearization.

"Decreasing the number of U.S. troops in South Korea should also never be on the summit table," he said, adding this would only heighten the possibility that North Korea may renege on an agreement that would come out of the summit.

Hong's LKP, formerly known as the Saenuri Party, was in power until May last year when it was defeated at the polls by the Democratic Party of current President Moon Jae In.

Public support for the conservative party plummeted after late 2016 when then President Park Geun Hye was impeached over a massive corruption scandal. She was subsequently convicted and sentenced to 24 years in prison.

The LKP currently holds 113 seats in the 300-member National Assembly.