SEOUL -- Former UN chief Ban Ki-moon on Wednesday vowed not to run for presidency in Republic of Korea, his home country, during an unscheduled press briefing in the parliament.

Ban told reporters that he will give up his "pure will" to lead the country's political change and the national unity, abandoning his ambition to become the next South Korean leader to replace the impeached president.

The former UN head has never officially declared any decision to run for presidency, but he has long been viewed as the most powerful presidential contender in the conservative bloc.

An early presidential election is widely forecast to be held in April or May as the motion to impeach President Park Geun-hye was passed in the National Assembly on Dec 9 with an overwhelming majority.

The press conference was urgently held without any prior notice. He returned to South Korea on Jan 12 after his second, five-year tenure in the top UN post terminated at the end of last year.

Since his comeback, Ban had made the so-called "people-friendly" trip across the country to directly meet people in regions. He also proposed to amend the country's constitution for decentralized presidential power.

His actions and words in the past three weeks pulled down his approval ratings for his mistakes in the nationwide campaign and local media speculations about his involvement in a bribery case involving his younger brother and nephew.

During the conference, Ban said that his pure patriotism and ambition were damaged by slanders and fake news reports that were almost equivalent to "killing" his personality.

The career diplomat said he was very disappointed at the narrow-minded, egoistic behaviors show in some of the political arena, noting that it would be meaningless for him to go together with them.

He expressed his deep apology to supporters, advisors and those working around him.

Ban, however, vowed to devote himself to resolving the country's crisis and bringing a bright future based on his experience as former UN chief.