US Secretary of State Condoleezza Rice was to hold talks next week with the UN on Zimbabwe, as Harare blamed Britain for a "genocidal" cholera outbreak and President Robert Mugabe ignored mounting calls to quit.
Rice will visit New York on Monday and Tuesday to discuss among other things the political deadlock in Zimbabwe, ravaged by a meltdown and a humanitarian crisis, State Department spokesman Sean McCormack said in Washington.
McCormack said Rice hoped the UN Security Council will work more forcefully to end the multiple crises in the southern African nation, ruled by Mugabe since its 1980 independence from Britain.
She wants Mugabe to step down, a move backed by US President George W. Bush and other world leaders, including British Prime Minister Gordon Brown and French President Nicolas Sarkozy.
"We're in discussions with members of the Security Council as to what the Security Council as a body might do," McCormack said Friday.
"And what we want to do is to start a process that will bring an end to the tragedy that is unfolding in Zimbabwe."
But Mugabe's government struck a combative tone as the World Health Organisation (WHO) said the death toll had risen to 792, and aid groups warned the epidemic could last for months .
"Cholera is a calculated, racist attack on Zimbabwe by the unrepentant former colonial power, which has enlisted support from its American and Western allies so that they can invade the country," Information Minister Sikhanyiso Ndlovu said.
"The cholera epidemic in Zimbabwe is a serious biological, chemical war force, a genocidal onslaught , on the people of Zimbabwe by the British," he said. "It's a genocide of our people."
One day earlier, Mugabe had proclaimed in a nationally broadcast speech that "there is no cholera" -- comments his spokesman George Charamba later said were meant as "sarcasm."
UN chief Ban Ki-moon meanwhile said he had met with the 84-year-old leader two weeks ago at a summit in Qatar, where he urged Mugabe to leave his legacy "in a positive way."
"Mugabe really should look for the future of his country and his own people, who have been suffering too much, too long from this political turmoil now coupled with very serious humanitarian tragedies," Ban said in Geneva.
But Ban said the meeting did not go well, calling the dialogue "very difficult."
The cholera epidemic is only the latest grim symptom of Zimbabwe's collapse.
The economy has crumbled under the world's highest inflation rate, last estimated in July at 231 million percent but now believed to be much higher.
A new 500 million dollar note, worth 10 US dollars (7.50 euros), was introduced Friday by the central bank, which struggles to print money fast enough to keep pace with prices that rise several times a day.
Due to currency shortages, cash can only be withdrawn once a week from banks, and then people are allowed to take only 500 million dollars, which is not enough to see them through the day.
Hospitals have no drugs, no equipment and no staff left to treat the cholera epidemic, which has spread as sewage and water lines have broken down, contaminating the drinking supply.
A political stalemate between Mugabe and opposition leader Morgan Tsvangirai has deepened the crisis and left the government in limbo.
The two signed a power-sharing deal three months ago after a controversial one-man presidential run-off won by Mugabe but have so far failed to agree on how to form a unity government.