Ban returned home last month after a decade in New York and was widely expected to run in elections due this year, but his putative candidacy ran into a series of stumbles and he struggled for backing.
"I will give up my pure intention to bring about a change in politics under my leadership and to unify the country," he told reporters at a hastily arranged press conference.
"I'm sorry for disappointing many people."
Reports claimed he had signed a contract to rent a 660-square metre office in Seoul, and as recently as yesterday he was urging a change to the constitution to dilute the sweeping executive powers of the presidency and ensure more co-operative governance.
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The 72-year-old was widely expected to join Park's Saenuri party or an emerging conservative breakaway group for presidential elections which are due this year, whatever the outcome of the impeachment process.
"I was very disappointed by the parochial, selfish attitudes of some politicians," he said today. "I reached a conclusion that it would be meaningless to move forward with them."
"In order to resolve our current problems, we need to abandon the self-conceited attitude of 'it must be me or no one else'," Ban added.
But he was also to some extent the author of his own misfortune, analysts said, not articulating a clear political platform and his prominent global role failing to translate into domestic support.
He was criticised for wearing head-to-toe protective gear to try out a disinfectant spray at a farm, when most of those around him were not similarly dressed, and came under fire for becoming infuriated with reporters who asked questions about a controversial agreement between South Korea and Japan on wartime sex slaves.
"My pure patriotism and aspirations have fallen victim to slander that was close to personality slaughter," he said Wednesday, before bowing briefly, shuffling his papers and leaving the stage to a barrage of camera flashes.
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