The United States and South Africa pledged joint action Friday to induce reforms in Zimbabwe as Secretary of State Hillary Clinton hailed a new spirit of cooperation between the two democracies.

Clinton, visiting Africa's largest economy on a seven-nation tour of the continent, said she did not come seeking promises but believed that South Africa had a strong role to play in Zimbabwe and other African hotspots.

"We're working together to realise the vision of a free, democratic and prosperous Zimbabwe," Clinton said after talks with South African International Relations Minister Maite Nkoana-Mashabane.

"We're going to be closely consulting as to how best to deal with what is a very difficult situation for South Africa and for the United States, but mostly for the people of Zimbabwe," Clinton told journalists.

The pledge signals a shift in tone between Pretoria and Washington with relations uneasy in recent years due to sharp disagreements over Zimbabwe, the fight against AIDS and the Iraq invasion, under former president Thabo Mbeki.

Aides to Clinton said they expect a more robust partnership between the two countries under US President Barack Obama and South African President Jacob Zuma, whom Clinton will meet Saturday as she criss-crosses across the country.

The US has been one of long-serving Zimbabwe President Robert Mugabe's fiercest critics, pushing for evidence of reforms under the new unity government with Prime Minister Morgan Tsvangirai.

Both the European Union and the US maintain a travel ban and asset freeze on Mugabe, his wife and inner circle in protest at controversial polls last year and alleged human rights abuses by his government.

"We are attempting to target the leaders of Zimbabwe with sanctions that we think might influence their behaviour without hurting the people of Zimbabwe," said Clinton.

The country's unity government has stemmed a devastating economic crisis since it formed February, but has been hit by claims of a crackdown on the former opposition and failure to agree on key posts.

The South African foreign minister said it was crucial to fast-track the full power-sharing agreement so that ordinary Zimbabweans -- already suffering from years of hyperinflation that rendered their currency worthless -- do not lose patience.

Nkoana-Mashabane said while she had not felt "a chill" in the era of Mbeki and former US president George W. Bush, the pushing forward of the bilateral relationship was exciting.

"We have agreed today that what has not been happening in the past eight years is that most of time our relations were happening without proper co-ordination," she said.

Zuma, who assumed the presidency in May, has in the past supported a tougher line on Zimbabwe than Mbeki, who had scoffed at US and British-led attempts to punish Mugabe and supported an African-led approach of engagement.

Clinton later headed to Johannesburg for a half-hour private meeting with Nelson Mandela, who became the first president of a multi-racial South Africa in 1994 and remains one of the world's most respected figures.

At a later meeting with business leaders, America's top diplomat said she supported a robust role for South Africa across the continent.

"The economic success of Africa hinges in no small part on the economic success of South Africa," she said.

Clinton later visited a part-US funded AIDS clinic and held a "very frank conversation" with health minister Aaron Motsoaledi, praising the new government's commitment to fight HIV which affects nearly six million South Africans.

Zuma's predecssor Mbeki drew intense world criticism for questioning HIV links with AIDS, while his government failed to roll out lifesaving anti-retrovirals quickly for one of the world's worst-affected populations.

"We have to make up for some lost time. But we're looking forward," Clinton said.