Nigerian Foreign Minister Ngozi Okonjo-Iweala has resigned, days after being replaced as head of the country's economic reform team.
Okonjo-Iweala was credited with securing debt relief
Mrs Okonjo-Iweala, who negotiated the cancellation of $30bn debt to the Paris Club, was moved in June from the Finance Ministry to Foreign Affairs.
She had remained head of the economics team, but this week was replaced by the new Finance Minister, Nenadi Usman.
President Olusegun Obasanjo praised the minister's "monumental achievements".
A government stated quoted the president as accepting Mrs Okonjo-Iweala's resignation "based on your compelling need to take care of pressing family issues".
Critics of the president say the change may be because of a personal clash.
Mrs Okonjo-Iweala's ousting as head of the economic reform team was announced while she was in London, trying to secure further debt relief for Nigeria.
The BBC's Mannir Dan Ali in Abuja says many Nigerians are unsurprised by her resignation from the foreign ministry, believing that someone with her experience could not be expected to tolerate the treatment she had received over the past few months.
A former top World Bank executive, it was as Nigeria's finance minister and head of President Obasanjo's economic reform team that Mrs Okonjo-Iweala made her name at home and abroad.
She saved - rather than squandered - the government's profits from oil revenues.
Then she negotiated the largest debt relief deal in Africa, which saw Nigeria's $30bn debt to the Paris Club partly written off, saving the country $18bn.
But without warning in June, she was suddenly switched from being the minister of finance to the prestigious, but less powerful position of foreign minister.
Analysts were concerned but were reassured by the fact that she retained her post as head of the economic team, from which she was removed earlier this week.
Mrs Usman, who succeeded her first as finance minister and then as head of the economic team, has pledged to keep the reform programme going.