Liberal presidential candidates and their campaign staff squared off Thursday over how to resume negotiations to pick a single candidate to compete against the ruling conservative hopeful in the December election.

Independent candidate Ahn Cheol-soo, who suspended ongoing talks the day before and accused the main opposition Democratic United Party (DUP) of trying to manipulate the selection process by spreading unfounded rumors, expressed deep disappointment over recent developments.

In a meeting with reporters, the entrepreneur-turned-politician warned that if there is no change, the liberal camp will not be able to win the presidential race this year.

"The process of reaching understanding on the single candidacy issue is much more important than the results," he said.

He added that only by going through a clear selection process, can both sides persuade voters to support a liberal candidate over conservative Saenuri Party contender Park Geun-hye when they go to the ballot on Dec. 19.

The 50-year-old candidate who is popular with young voters said while he wanted to apologize to the people for the suspension of negotiations, the action was taken to call on the DUP to approach the single candidacy issue from a broader perspective.

"If the process is only viewed as competition, then even if one candidate is picked, he will not be able to win the presidency," he claimed.

Ahn has consistently emphasized the merging of values and policies.

Talks were halted when Ahn's election camp attacked Moon and his supporters for allegedly spreading lies that Ahn will give up his candidacy for Moon on the promise of a power sharing arrangement, if the liberal camp wins the presidency. 

Such a move implies that Ahn will concede the candidacy to Moon and may have started affecting the independent's standing in recent polls.

Camp officials said that the DUP has also launched personal attacks against one of Ahn's representative at the single candidacy talks, and violated an agreement not to announce what future actions need to be taken before approval by both sides in advance.

In response, Moon said during his trip to Busan, 453 kilometers southeast of Seoul, that he will apologize for any words or deeds made by his aides.

"If offense was given inadvertently by aides, I would like to extend my apology," he said. The former human rights lawyer and chief of staff to late President Roh Moo-hyun said efforts are under way to restart talks as soon as possible, because there is not enough time before the Nov. 26 merger deadline.

Moon too said he was sorry for causing the commotion, but pointed out all merger talks have their "ups and downs" and can hit snags.

DUP officials said they held an emergency meeting of key policymakers earlier in the day, and are trying to resolve the issue as soon as possible.

The need to contact Ahn's election camp has gained urgency because delaying the resumption of single candidacy talks may force Moon to accept a nationwide survey to decide on the candidate, which may be disadvantageous to the DUP contender. Moon has called for mixing the result of several polls with an open primary arrangement.

On the other hand, some campaigners believe that Ahn intentionally disrupted the talks after a few polls started showing Moon moving ahead of his rival.

The ruling Saenuri Party, meanwhile, attacked the single candidacy process as a political show to trick voters into picking a candidate whose credentials in running a country have never been proven.

Moon, a first term lawmaker has only limited public experience having only held several senior secretarial position under President Roh. Ahn has never held office, having founded AhnLab, the country's largest anti-virus software company, and having taught at two local universities.

Kim Moo-sung, the head of Saenuri's election strategy office, said the sudden suspension of talks shows that Ahn has finally learned that he is being exploited by the DUP.

"The outcome of the single candidacy talks was pre-ordained with Ahn being used as kindling wood by Moon to win public support so he can grab power," he said, claiming that the DUP cannot be trusted because it always says one thing and acts in a completely different manner.

Besides criticizing the merger talks in general, the Saenuri Party stepped up its war of words over the controversy surrounding the de facto sea border between South and North Korea that can hurt the DUP presidential candidate.

Saenuri claimed that President Roh disavowed the Northern Limit Line during the 2007 summit held in North Korea. The conservative party said such a statement is tantamount to surrendering national sovereignty and DUP presidential hopeful Moon Jae-in must come forward with the truth on the allegations raised.

Moon was Roh's chief of staff at the time of the summit and played a key role in arranging the meeting.

In addition the party claimed Moon took part in an attempt to prevent regulatory inspection of a savings bank that eventually went bankrupt.

On the savings bank issue, party officials said the DUP candidate and the law firm he represented won 7 billion won ($6.4 million) worth of cases after Moon interceded on behalf of the failed financial institution.

Moon has refuted both charges as untrue and a move by Saenuri to engage in mud-slinging tactics. (Yonhap News)