(CNN) -- One of Zimbabwe's top officials blamed his country's spreading cholera outbreak on what he calls "a genocidal onslaught" by Zimbabwe's former colonial ruler -- Britain.

Zimbabwean clinics have been overwhelmed by the cholera epidemic, according to aid organizations.

"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 told reporters. Britain ruled the country as a colony until 1965.

Ndlovu's claims triggered quick and pointed reaction from Britain and the United States.

In Washington, State Department spokesman Rob McInturff called Ndlovu's accusations "patently ridiculous."

Referring to Zimbabwean President Robert Mugabe, McInturff said Friday that, "Mugabe is clearly unwilling to take any meaningful action (to stop the cholera outbreak)."

On Thursday, Mugabe said "there is no cholera in the country." His spokesman later said that Mugabe was sarcastically ridiculing what he believes are Western designs to invade the country.

Britain's Africa minister, Mark Malloch-Brown responded by saying, "I don't know what world he (Mugabe) is living in," according to the British newspaper The Guardian.

Malloch-Brown made the comment during a one-day trip to South Africa, where he visited a Johannesburg church housing 1,600 Zimbabweans who have fled their country, the newspaper said.

"There is a raging humanitarian crisis in Zimbabwe as well as an economic crisis and still there is no representative government able to lead the country out of this disaster," he said, according to The Guardian.

Cholera has ravaged Zimbabwe, causing nearly 800 deaths and infecting more than 16,000 people, the World Health Organization says.

The outbreak could surpass 60 000 cases, according to an estimate by the Zimbabwe Health Cluster, which is a group coordinated by the World Health Organization.  View image gallery of Zimbabwe's cholera crisis Â»

Cholera, a bacterial waterborne disease that causes diarrhea, dehydration and, if not treated, death in a matter of hours, is widespread in Zimbabwe but help is not.

Like the general Zimbabwean economy, the country's health delivery system is strapped, lacking modern drugs and machinery, while doctors and nurses have been striking for over a month.

On Friday, the State Department issued a travel warning for U.S. citizens because of the cholera outbreak and violence that has flared as Zimbabwe's economy has deteriorated.

"The public health system in Zimbabwe no longer provides even basic services due to a lack of staff, electricity, clean water, and medical supplies," the travel warning said. "Americans who fall ill while in Zimbabwe may find it difficult to find treatment."

At the State Department's daily press briefing Friday, spokesman Sean McCormack said the situation in Zimbabwe will be one of the topics Secretary of State Condoleezza Rice will discuss when she visits the United Nations next week.

"The number of cases of cholera -- statements from Robert Mugabe notwithstanding -- is going up, not down," McCormack said. "The crisis has not ended. People's lives are in danger."

Health experts say the Zimbabwean government can win the battle against cholera only if it imports adequate stocks of water-treating chemicals and disposes of refuse and sewerage properly.  Watch shocking footage of Zimbabwe's humanitarian crisis (Discretion advised) Â»

A Doctors Without Borders epidemiologist in Zimbabwe said, referring to the capital city, that "the scale and sheer numbers of infection, especially in Harare, is unprecedented." He said the group has treated more than 11,000 patients since August and has 500 international and local staff members treating people in cholera centers across the country.

He said the main reasons for the outbreak are poor access to clean water, uncollected garbage in the streets and burst and blocked sewage systems.

"The fact that the outbreak has become so large is an indication that the country's health system can't cope," he said.

Meanwhile, in his statement Thursday Mugabe said, "I am
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