UN Chief could win S.Korean presidency

But vying for the December 2017 election would cast Ban into a political arena far more bruising than the genteel give-and-take of global diplomacy to which he is accustomed, exposing his family, finances and career to intense scrutiny.

Ban is coy about his plans.

He told Reuters on Friday that he will decide on his future when he returns to South Korea in January after his U.N. tenure finishes at the end of the year.

But in his clearest statement yet on his intentions, he said he was conscious of "expectations from many people in Korea that I should make myself available for a better future of Korea."

With the pride Koreans take in him as "president of the world" and absence thus far of strong competition, opinion polls show Ban as the front-runner for the election next year.

However, his lack of a political base, a decade-long absence from South Korea to lead the United Nations, and his age - he is 72 - are potential liabilities.

Kim Chong-in, former leader of the opposition Democratic Party of Korea, said Ban many not be able to run a rigorous campaign after having been away for so long.

"In this day and age when the world changes so quickly and people's way of thinking changes dramatically, is it going to be easy for him to even grasp the reality here?" Kim said.

Some U.N. diplomats say the gentlemanly Ban has been a weak leader.

"He hasn't had the ability to really drive international opinion on any of these big issues and he's tried to do the job as sort of best friends of every member state," said a senior U.N. diplomat, speaking on condition of anonymity.

"You can't do that when there's a morally right position and a morally wrong position."

Ban rejects the characterisation that he is not a strong leader, arguing that he has stood up against injustice and violations of human rights and spoken up more strongly than other world leaders for the common good.

He said there was a misperception that a charismatic style was needed for effective leadership, and that there were "serious misunderstandings" about his leadership style.

"There are many different leadership styles," Ban said in an interview in his office at U.N. headquarters in New York.