By Barnaby Phillips
BBC News, Johannesburg
The US has again condemned what it calls tyranny in Zimbabwe, saying Southern African countries should be tougher on human rights abuses.
The US says Mugabe's Zimbabwe is an "outpost of tyranny"
Earlier this week, South African President Thabo Mbeki said American criticism of Zimbabwe was exaggerated.
Now the US ambassador to South Africa has contrasted the decisive approach of West African States towards Togo with South Africa's approach to Zimbabwe.
The remarks confirm Washington's determined stance towards Zimbabwe.
In an address to a university in Johannesburg, Jendayi Fraser said the fact that countries in the region are not speaking out about repression in Zimbabwe made it difficult for supporters of Africa in the American government to argue the case for more aid.
The Secretary of State, Condoleezza Rice, recently named Zimbabwe as an "outpost of tyranny" in a list that included North Korea and Iran.
Mr Mbeki favours an approach of quiet diplomacy
President Thabo Mbeki of South Africa has a different approach.
This week he said his relations with President Robert Mugabe are very good and that Zimbabwe should not be on a list of countries where there is tyranny.
Zimbabwe is holding elections in March.
Observers from South Africa have been invited - but Zimbabwe will not allow observers from the American government or European Union.