The leaders of two minor opposition parties declared their merger to chart a new middle-of-the-road political group Thursday despite deepening internal dissension and defections.

Ahn Cheol-soo of the center-left People's Party and Yoo Seong-min of the center-right Bareun Party hastily arranged a press conference to announce their merger plan, which they think will bolster their parliamentary foothold ahead of the June gubernatorial and mayoral elections.

Dissenters in both parties opposed the integration, citing their different ideological leanings and policy stances, particularly on how to handle an increasingly provocative North Korea.

"We, two people, as the leaders of the parties, decided to make efforts for the success of a new unified, reformist party despite any difficulties," they said in a joint statement.

They then vowed to break with "old, corrupt, factional and outmoded" politics and bring together "reform-minded conservatives and rational centrists" to live up to people's aspirations for political reform.

"The new unified reformist party will be a party never seen before in our politics," they said.

"We will become a political force that drives out conservatives only angling for power, and extreme conservatives, and fulfills its inherent political responsibility to take care of people's livelihoods. We will present capable alternative politics," they added.

The merger will create a party with 48 parliamentary seats in the 299-member National Assembly. It is seen as a prelude to a major political realignment ahead of the local elections, which are seen as a public referendum on President Moon Jae-in's first year in office.

The pair also used the press conference to outline their policy visions.

They pledged to ensure watertight security; prioritize deterring war and resolving the nuclear standoff with North Korea based on a solid South Korea-U.S. alliance; and foster a "free, fair" market economy.

Both parties have been caught in intense infighting over the merger.

Some senior members of the People's Party have rejected the scheme, arguing it would obscure the party's political identity and irk core supporters in its stronghold of the southwestern Honam region.

Division within the Bareun Party ran deeper, triggering the recent defection of three key members.

Various opinion polls show that the union between the two parties will jack up their combined public support to a level strong enough to take on the two major parties -- the ruling Democratic Party and the main opposition Liberty Korea Party.

The merger move apparently grated with the two major parties.

"The union, fraught with scars, will be their shelter only for survival, and will not last long," LKP spokesman Chang Je-won told reporters.

"It is antinomic for the two leaders, who cannot even foster unity within their party ranks, to seek a union between their parties," he added.

The ruling party belittled the merger as a "political regrouping with no justification." (Yonhap)