The United Nations special investigator on torture has been deported from Zimbabwe after being detained at Harare airport.
Manfred Nowak was refused entry despite having a written invitation from Prime Minister Morgan Tsvangirai.
Mr Nowak told the BBC he blamed his treatment on divisions within the unity government.
He told the World Today programme his treatment showed there were clearly parts of the government who did not want him to assess "the current conditions of torture".
Mr Nowak says he had never been treated in such a manner in any other country and promised to file a strongly worded complaint.