South Africa's Desmond Tutu has accused his country of betraying its anti-apartheid legacy by failing to take strong action against Zimbabwe's President Robert Mugabe.
Archbishop emeritus Tutu, a Nobel peace prize winner, also says that military force against Mr Mugabe's government should not be ruled out.
"How much more suffering is going to make us say 'No, we have given Mr Mugabe enough time?'," he asked in an interview with BBC Radio 4.
While neighbouring countries Botswana and Zambia have taken a tough line against the Mugabe regime, South Africa has stopped short of calling on him to quit. It has strong historic links with Mr Mugabe, who provided support during the struggle against apartheid.
Mr Tutu also criticised South Africa for not taking tougher stands at the United Nations against countries with a record of human rights abuses.
"I am deeply, deeply distressed that we should be found not on the side of the ones who are suffering," he said.
"I certainly am ashamed of what they've done in the United Nations."
Alleged plot to overthrow Mugabe
A former Zimbabwean newscaster and nine other opposition activists are expected to face charges of plotting to overthrow the Mugabe government.
Jestina Mukoko, head of the Zimbabwe Peace Project, was taken away at gunpoint in Harare on 3 December by unidentified men and the High Court has ordered police to find her. Police have previously said Ms Mukoko was not in their custody.
The state-run Herald newspaper says the activists are being charged with recruiting or attempting to recruit people to undergo military training to topple the government.
It says the plan was to "forcibly depose" the government and replace it with one headed by opposition Movement for Democratic Change leader Morgan Tsvangirai.