Speaking on Thursday, Manfred Nowak said Zimbabwe's behaviour was 'unacceptable'
The failed attempt by the UN's torture investigator Manfred Nowak to visit Zimbabwe was "calculated" to provoke, a Zanu-PF minister has said.
He was held overnight at Harare airport on Wednesday and returned to South Africa as he had no clearance to visit.
He insisted he had an invite from the prime minister and blamed his treatment on divisions in the unity government.
But Foreign Minister Simbarashe Mumbengegwi said Mr Nowak had been officially asked to postpone his visit.
Prime Minister Morgan Tsvangirai and his MDC party stopped co-operating with the unity government two weeks ago, accusing President Robert Mugabe's Zanu-PF party of failing to live up to its power-sharing commitments.
The invitation by the prime minister was a nullity
Mr Nowak's original invitation was withdrawn at the last minute, with officials citing a clash with a visit by a regional mediation team to help resolve the crisis.
Mr Tsvangirai intervened and authorised the UN investigator to proceed with his visit.
"The invitation by the prime minister was a nullity," AP quotes Mr Mumbengegwi as saying.
"This was a calculated move to create a diplomatic incident."
Mr Nowak was to meet officials and rights activists, and inspect prisons and police stations during a week-long visit. He was tasked with compiling a report for the UN Security Council following reports of MDC harassment.
World Cup fears
Andrew Harding BBC News, Harare
Foreign envoys have been shuttling around Harare like marriage guidance counsellors. They are trying to save the dysfunctional relationship that passes for a government.
For eight months, Robert Mugabe and his long-time rival Morgan Tsvangirai, have been sharing power - after a fashion. Their political truce has allowed the strangled economy to start breathing once again. But the alliance is now on the rocks as the MDC accuses President Mugabe of multiple violations of what you might call their prenuptial agreement.
The courts and the security services remain very much in his control. MDC officials have been arrested, abducted and beaten. And Mr Tsvangirai may be prime minister, but he has been humiliated by the treatment of the UN torture envoy.
Mr Mugabe's Zanu-PF insists it is committed to sharing power. But the MDC is threatening to pull out altogether and trigger new elections. Right now, that still seems unlikely. The alliance, for all its faults, remains the best deal on the table.
According to the AFP news agency, the foreign minister said Mr Nowak would be able to rearrange his visit "at a mutually agreed time in spite of this unwarranted, provocative act".
Southern African Development Community (SADC) mediators are reportedly to meet Mr Mugabe and Mr Tsvangirai separately on Friday.
Justice Minister Patrick Chinamasa, from Mr Mugabe's party, said he had told the mediators on Thursday he felt the MDC was responsible for the political crisis, and outstanding power-sharing issues were minor.
"We did also emphasise in our meeting that we feel that we are more wronged than being the wrong-doers in this regard," he told the BBC's Network Africa programme.
Earlier this week, Zanu-PF described comments about allegations of violent attacks on MDC members as "cheap propaganda".
The BBC's Andrew Harding in Harare says Zimbabwe's neighbour South Africa will be keen to see coalition partners find a way of working together.
In the past South Africa has been accused of sitting lamely on the sidelines as Zimbabwe's political crisis has unfolded.
But our correspondent says that now it has the football World Cup to host next year, it does not want a new crisis in Zimbabwe to spoil the party.
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