Opposition leader Morgan Tsvangirai won a clear victory over President Robert Mugabe in last month's disputed elections in Zimbabwe, the top US envoy to Africa said on Thursday.

"The most credible results we have today are a clear victory for Morgan Tsvangirai in the first round and maybe a total victory," US Assistant Secretary of State Jendayi Frazer told reporters in South Africa.

"According to what we know, Morgan won in the first round and there should be a change," she said.

AFP