Nigeria's police chief Tafa Balogun has announced he is retiring in March and going on leave with immediate effect.
The announcement, made in a government statement late on Monday, has shocked commentators, a BBC correspondent says.
President Olusegun Obasanjo wished Mr Balogun a happy retirement and thanked him for his service.
No official reason was given for the decision, but Nigeria's anti-corruption boss said Mr Balogun was asked to stand down following corruption allegations.
"It's the work we carried out which led to the government taking that decision," Nigerian Economic and Financial Crimes Commission (ECFCC) boss Nuhu Ribadu told the BBC's Hausa service.
He said an investigation is examining allegations that Mr Balogun had large sums of money in a Lagos bank account.
Mr Ribadu added that investigations were continuing.
Mr Balogun - who has been police inspector-general for the last three years and in the police force for more than 28 years - has been unavailable for comment.
'At ease'
Mr Balogun's successor is Deputy Inspector General Sunday Ehindero, who takes over immediately, the statement said.
" I am surprised by the development "
"I am surprised by the development. I cannot talk now. I am trying to return to Abuja where I hope to assess the situation," he told Nigeria's Guardian newspaper.
According to the BBC's Yusuf Sarki Muhammad, the police boss gave no hint about his impending retirement on Monday morning at a ceremony in Abuja to decorate recently promoted police officers.
He was at ease and posed for press photographs, our correspondent says.
President Obasanjo has been vocal in his commitment to tackling corruption since taking office in 1999.
Out of 146 countries, Transparency International last year ranked Nigeria as the third most corrupt country in the world.
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