A UN independent torture expert said Wednesday he will travel to Zimbabwe to meet Prime Minister Morgan Tsvangirai despite the government's last-minute withdrawal of an unprecedented invitation.

"I am going to Zimbabwe tonight. I will meet the prime minister tomorrow at 10," Manfred Nowak, UN special rapporteur on torture and cruel, inhuman and degrading treatment told a press conference in Johannesburg.

"I expect to meet him tomorrow and then I hope that we can define in what terms the mission will go and for how long."

The Zimbabwe government on Monday withdraw its October 1 invitation for the eight-day mission set to start Wednesday, amid a renewed political crisis between power-sharing rivals Tsvangirai and President Robert Mugabe.

However, informed of the U-turn on arriving in neighbouring South Africa Tuesday, Nowak said he was invited the same day to meet Tsvangirai in an originally planned session on Thursday.

"Receiving two completely different messages, one via the Zimbabwe mission in Geneva and one directly from Harare from the head of the government," he said.

"I got the clear message from the prime minister that it is his understanding that the mission is going on. That leads me to the conclusion that there must be some kind of misunderstanding between the different cabinet members."

Harare suddenly announced that it could not maintain the proposed dates citing a "previously unanticipated consultative process" with the Southern African Development Community (SADC).

The shift came as Tsvangirai and ministers drawn from his Movement for Democratic Change (MDC) party boycotted a cabinet meeting led by Mugabe for the second time.

Tsvangirai has suspended ties with the 85-year-old until all unresolved issues in the government's unity pact are ironed out which include disputes over key posts and a crackdown against his supporters.

Earlier this month, Nowak had announced the invitation to check on conditions in Zimbabwe earlier this month, welcoming it as a sign that the government was willing to open dialogue on human rights and allow "unfettered access" to detention centres.

The UN human rights office on Wednesday underlined the urgency of the fact-finding mission, highlighting allegations that MDC supporters had been arrested and intimidated in recent days.

Nowak said the last minute postponement was not "the way one should deal with the United Nations" and that he hoped to meet other members of the unity government once in Harare.

The SADC meeting was not a valid reason to postpone the eight day trip, he said.

"I still count on the understanding and hope for the understanding of the government ... I mean the entire government of Zimbabwe to receive me in a cooperative spirit," he said.