The main opposition Liberty Korea Party said Friday it will seek to revise the Constitution with a focus on delegating more presidential power to the prime minister and suggested the rival parties submit a joint revision bill to the National Assembly by June.

Rep. Kim Sung-tae, floor leader of the party, unveiled the party's road map for amending the basic law as President Moon Jae-in increased pressure on opposition parties to come up with a joint revision proposal as early as possible so that it can be put to a national referendum at the same time as June's local elections.

Kim's proposal to reach a revision deal by June reaffirms the party's rejection of Moon's timeline.

Moon's office expressed regret.

"After all, this means (the LKP) cannot agree to hold June's local elections and a national referendum at the same time. It's very regrettable," a Cheong Wa Dae official told reporters.

The ruling Democratic Party bristled at the LKP's proposal, denouncing it as a stalling tactic aimed at derailing the proposed June referendum. It also said there is no reason to push back a referendum until after the local elections, as agreement on key revision points is not expected to be difficult to reach.

The road map centers on making changes to the current presidential system that has long been accused of concentrating too much power on the president in a way prone to corruption. Critics and the media have portrayed the current system as "imperialistic."

The LKP's idea is that the president is elected by popular vote and represents the country, but the powers of the prime minister are significantly strengthened. The party didn't specify how the prime minister should be selected, but party officials have said they prefer having the National Assembly elect the prime minister.

Currently, the prime minister is named by the president.

The Cheong Wa Dae official also rejected the LKP's idea about strengthening the prime minister's power and having the National Assembly elect or recommend who should take the job, saying it is no different from the parliamentary cabinet system.

"In that case, the prime minister will remain only a symbolic figure and the prime minister will take charge of state affairs," the official said, adding that giving the parliament the right to name or recommend the prime minister would be hurting the separation of powers on which the Constitution is based.

Moon has strongly pushed to hold a referendum on a constitutional revision at the same time as June's gubernatorial and mayoral elections, saying now is the best time to revise the basic law, as the push for a revision would lose steam after the local elections.

The LKP has opposed the idea, arguing that holding the polls at the same time would run the risk of politicizing the issue and that the revision needs sufficient deliberations.

Earlier this week, Moon said the government would submit its own constitutional revision bill to the National Assembly by next Wednesday so that a referendum can take place on June 13 after two months of parliamentary deliberations and other administrative procedures.

If a revision bill is submitted next Wednesday, the National Assembly is required to vote on it by May 19. The bill needs approval from two-thirds of the 293 lawmakers in parliament to pass. The bill would then be put to a national referendum.

Even if the government submits its own revision bill, however, chances are not high for it to pass because the main opposition party has 116 lawmakers, more than the one-third of lawmakers required to reject the bill.(Yonhap)