Former UN chief Ban Ki-moon on Wednesday renewed his strong presidential ambitions, highlighting his likely campaign credo of "grand national integration," boasting of his diplomatic chops and bashing his rival for ambivalence on a key security issue.

During his appearance at a debate hosted by the Kwanhun Club, an association of senior journalists, Ban also reiterated his support for a constitutional revision to enact a "power-sharing" governance model that can reduce powers currently concentrated in a single leader. 

"Our country must stop the infighting and pursue grand national integration so as to make another new leap forward," Ban said during his opening remarks. "That is the zeitgeist of this year's presidential election and justice."

In another show of his determination to run for the country's top elected office, Ban said he has decided to give his all to achieve a "change in politics," a phrase he has repeatedly used in a swipe at establishment politicians mired in partisanship, factionalism and ideological feuds.

Ban, however, said he does not have any "personal greed" for a powerful state position.

"I am not trying to become something or coveting a position, but I have decided to give my all for the veritable change in politics so as to lead our country to become a light in the world again and to give hope to our citizens," he said.

Saying the country is facing the double whammy of security and economic challenges, he stressed his extensive network with foreign leaders, experience as a leader of a world body and his diplomatic skills.

"We are in an era when the economy and diplomacy are inseparable," he said, indicating that the country can help address economic challenges through diplomacy. "It is the time that calls for (a leader) with a network with global leaders and extensive experience on the world stage."

Asked when he made a decision related to the presidential election, Ban said he reached the decision in December when President Park Geun-hye was impeached over a corruption scandal involving her and her friend Choi Soon-sil.

"(I made the decision) because a very unfortunate thing happened in Korea due to the scandal and the impeachment of the president," he said. 

On the issue of a constitutional revision, Ban pointed to the need for the review of a power-sharing system that allows a president to serve for up to two consecutive years. Ban has long championed a revision that would enable the diffusion of power.

"In fact, the president is a human being whose capabilities are limited, though under the current presidential system, the chief executive has taken charge of all -- domestic and external affairs," Ban said.  

Ban also slammed his rival Moon Jae-in, a former leader of the main opposition Democratic Party, for an apparent shift in his stance over the planned deployment of a US missile defense system to South Korea. 

Moon, who used to remain opposed to the plan to deploy a Terminal High-Altitude Area Defense system to the peninsula, is now seen as softening his stance. He has recently said in a media interview that the plan cannot easily be canceled.

"(Moon) has been going back and forth (over the THAAD issue). As criticism rises, he is now reversing himself," Ban said.

Commenting on Seoul's decision to shut down an inter-Korean industrial complex in the North's border city of Kaesong, Ban said it was an "inevitable decision" at a time when the safety of South Koreans was endangered due to Pyongyang's military threats. (Yonhap)