Harare — A senior leader in President Robert Mugabe's Zanu PF has unexpectedly resigned sparking fears of a fresh battle to succeed the ageing leader during the ongoing party congress.

Mr Mugabe had looked secure after he played another tough balancing act ahead of the congress that opened on Thursday by silencing the several factions angling for his job.Protesting against

But Mr Basil Nyabadza, a provincial chairman threw in the towel protesting against the nominations for the party's top four posts, which he said lacked transparency.

His resignation letter also raised the issue of tribalism, a scourge that threatens to tear apart the former liberation movement.

Mr Nyabadza's Manicaland province had wanted Zanu PF secretary for administration Mr Didymus Mutasa to take over as chairman.

But Mr Mugabe was forced to push for the elevation of Zimbabwe's Ambassador to South Africa, Mr Simon Khaya Moyo to the fourth most senior position to rescue a 1987 Unity Accord with PF Zapu.

The accord that ended the 1980s conflict in south western parts of Zimbabwe that claimed the lives of more than 20,000 civilians provides for the two parties to share the four posts in the provinces equally.

President Mugabe and his deputy Ms Joice Mujuru represent the old Zanu PF while the new Vice President John Nkomo and Mr Moyo will represent PF Zapu.

Meanwhile, Zimbabwe's 2008 elections were marred by the widespread rape of political opponents by President Robert Mugabe's supporters, according to a report released by an HIV/Aids advocacy group on Thursday.

The report prepared by Aids-Free World says Mr Mugabe's supporters, including youth militia and some veterans of Zimbabwe's 1970s independence war, "committed widespread, systematic rape in 2008 to terrorise the political opposition."