UN torture expert Manfred Nowak said his expulsion from Zimbabwe on Thursday showed that the country's unity government "does not function", in an interview with AFP.

"The government, as a unity government, does not function," he said shortly after arriving in Johannesburg from Harare.

"It sheds a very negative light on the functioning of the government."

Nowak was detained on his arrival late Wednesday in Harare, where he had planned to begin an eight-day mission to investigate alleged human rights abuses and arrests of political activists opposed to President Robert Mugabe.

He was expelled early Thursday, despite having received an official invitation from Prime Minister Morgan Tsvangirai, Mugabe's partner in a shaky unity government.