Harare - Manfred Nowak, United Nations special rapporteur on torture, was being detained Wednesday night at Harare airport as President Robert Mugabe's administration appeared to try to prevent his latest mission.

Nowak was invited in February by Justice Minister Patrick Chinamasa to Harare after reported widespread torture by Mugabe's security forces. On arrival late Wednesday, immigration officials refused to allow Nowak through, claiming he had no security clearance, he told the German Press Agency dpa by telephone from the airport immigration office.

"I should say I have never been treated in any other country in this way," said Nowak, who became special rapporteur in 2004. "This is a major diplomatic incident."

His visit coincided with a sudden worsening of relations within Zimbabwe's coalition government, between Mugabe and Prime Minister Morgan Tsvangirai, who says he has disengaged from dealing with Mugabe's ministers until the 85-year-old leader agrees to democratic reforms.

Officials of local human-rights organizations said they became alarmed late last week when they learnt that the Justice Ministry had not prepared any programme for Nowak.

Then, shortly before he was due to leave his headquarters in Geneva for Southern Africa, Nowak was called by the Zimbabwean embassy in Switzerland to be told that his trip was being postponed, claiming the visit would conflict with a visit by three foreign ministers from the Southern African Development Community, the 15- country regional bloc.

Nowak planned to spend a week in Zimbabwe, while the foreign ministers were on a one-day visit, diplomatic sources confirmed. "It's pretty clear that Mugabe realized belatedly that he didn't want Nowak," said one diplomat.

Nowak told dpa that he boarded his flight to Johannesburg and then asked Tsvangirai to facilitate his visit. The prime minister's office responded with a letter welcoming him to a meeting Thursday and said all the necessary arrangements had been made.

However, when Nowak stepped off the plane in Harare, Foreign Minister Simbarashe Membengegwi could be seen welcoming the three foreign ministers and escorting them to the airport VIP lounge. He took no apparent notice of the three UN officials who had started to argue with immigration officials.

"They told us if we did not get clearance, we would have to take the next flight out," Nowak said. "The next flight was due to leave at 7 am on Thursday."

The local UN office sent only a junior security officer to meet the delegation, but he was dismissed by the immigration officers. Nowak said when he called the Foreign Ministry protocol officer whom he expected to meet him at the airport, "the officer said he couldn't find us and went home."

No one from Tsvangirai's MDC party was there, either. An MDC official, contacted by journalists about 90 minutes after Nowak arrived, said that a senior member of Tsvangirai's office was on his way to the airport. (dpa)