Burundi Vice-President Alice Nzomukunda has resigned over corruption and human rights abuses that she says are hampering her nation's progress.
Mrs Nzomukunda said it had been a hard decision to resign
She also cast doubt on an alleged coup plot, which is rocking the country.
Former President Domitien Ndayizeye has been arrested in connection with the plot but Mrs Nzomukunda said she was not aware of any evidence of the plot.
Former rebel leader Pierre Nkurunziza was elected president last year under a deal aimed at ending the conflict.
Mrs Nzomukunda is from Mr Nkurunziza's mainly Hutu FDD party.
"My decision was motivated by numerous political problems which Burundian people are undergoing - problems of security, of not respecting the law, the management of state finances and of human rights laws which are violated," she said.
"The country was on a good path to overcome all these problems, but corruption and economic embezzlement are undermining it," she said.
Mrs Nzomukunda also told a press conference that she had taken the hard decision to quit the government after a year of humiliating interference in her work by party chairman Radjab Hussein.
She said she had complained to both the president and to the party's chairman himself, to no avail.
Since independence in 1961, Burundi has been plagued by tension between the dominant Tutsi minority and the Hutu majority.
Most Hutu rebel groups, such as the FDD, have joined the peace process but the FNL still refuses to lay down its arms.
More than 300,000 people have died in the war sparked in 1993 by the assassination of Burundi's first Hutu head of state and democratically-elected president, Melchior Ndadaye.