Rep. Ahn Chul-soo, an opposition heavyweight, on Sunday rejected an offer of a joint leadership system, calling for an early convention to select a new leader.

Rep. Moon Jae-in, head of the main opposition New Politics Alliance for Democracy, earlier proposed a three-way joint leadership with Ahn and Seoul Mayor Park Won-soon.

The offer was a desperate bid to end drawn-out internal wrangling and win the minds of voters.

A sense of crisis is palpable inside the liberal party ahead of the general elections slated for April next year.

Some analysis shows the NPAD will get only 70-80 seats in the 300-member parliament.

Moon, Ahn and Park, all considered as presidential aspirants, have come under growing pressure to save the embattled party, which has lost a series of recent elections to the ruling Saenuri Party.

Park accepted Moon's suggestion.

But Ahn, an entrepreneur-turned-politician, stressed Moon's offer is insufficient.

"More audacious and fundamental changes are necessary," he said in a press conference at the National Assembly.

He counter-proposed a "reform convention" to compete with Moon and other party members seeking the leadership of the party.

"To say nothing of the 2017 presidential elections, the outlook for the 2016 general elections is gloomy," he said. "Bigger changes are needed."

Moon immediately expressed regret over Ahn's decision, saying he still believes a joint leadership system is "the most realistic way" for reform and unity of the party.

"It's regrettable," he told reporters.

As to Ahn's proposal, Moon said he would make a decision after "listening to opinions" of party officials. (Yonhap)