Lee Jae-myung, the leader of the main opposition Democratic Party of Korea, attends at a party meeting held at the National Assembly in Seoul, Monday. (Yonhap)

Facing a series of prosecutorial investigations, the main opposition Democratic Party of Korea leader Lee Jae-myung said Monday he would comply with the prosecution's summon over an investigation into alleged bribery, but not on Wednesday as prosecutors originally requested.

"I don't understand the prosecution's behavior, but will confidently deal with (the case)," he told reporters at the National Assembly. "As you know, the case has already been cleared," he said, adding that he had prescheduled activities on Wednesday.

The opposition leader is currently under pressure to accept a summon by the prosecution on allegations that he received bribes through the soccer team FC Seongnam when he was the mayor of Seongnam, Gyeonggi Province.

He will consult with the prosecution to set a new date, he added.

Lee plans to visit South Jeolla Province on Tuesday and Gwangju on Wednesday to meet with citizens and ask for support. Lee's aides said he would continue his tour, visiting South Gyeongsang Province and surrounding cities in the first week of January next year.

The remark came hours after he blasted the Yoon Seok-yeol government for including former President Lee Myung-bak on the presidential clemency list, calling it a preferential decision that hinders national unity.

"(This amnesty plan) is not about national unity, but an unfair and ignorant decision favoring one side. Unfair abuse of power is an evil that destroys the people’s sovereignty," Lee said.

The Democratic Party leader and former presidential candidate criticized the government's decision to recommend a presidential pardon for former President Lee, who was sentenced to 17 years in prison for embezzlement and bribery. He has been imprisoned since October 2020.

Since his election as party leader in August, Lee has maintained a low-key stance as the prosecution carried out investigations into bribery and embezzlement allegations involving him.

With his legal troubles straining the Democratic Party's unity, Lee appears to have been seeking a breakthrough. His stepping up of criticism against Yoon and the prosecution, as well as seeking a reunion with liberal-leaning former President Moon Jae-in seem to be a part of such efforts, according to local reports and political commentators.

"They are also accelerating investigations targeting the former government, including its probe into North Korea's killing of a South Korean official in the West Sea and the termination of a nuclear reactor ahead of its expiration date," Lee said at a party meeting on Friday, suggesting that he and Moon are being targeted together by the prosecution.

"I will fight at the forefront against this shameless, fabricated investigation into the opposition party, and will proudly win," Lee added.

Meanwhile, the ruling People Power Party urged Lee to cooperate with the prosecution's summon.

The ruling party’s interim chief Rep. Chung Jin-suk on Monday called on Lee to appear for the prosecution’s summon. "I hope Lee will keep his promise to 'fight the prosecution's investigation proudly,’" Chung said in Facebook post, suggesting that Lee should face the allegations head-on instead of avoiding them.