Zimbabwe's information minister insisted on Tuesday the epidemic was "under control".

The government has accused Britain and the US of planning an invasion, as pressure mounts for Robert Mugabe, the president, to step down amid the deteriorating health situation, food shortages and economic collpase.

"The British and the Americans are dead set on bringing Zimbabwe back to the UN Security Council," George Charamba, a presidential spokesman, said in the state-run Herald newspaper.

"They are also dead set on ensuring that there is an invasion of Zimbabwe but without themselves carrying it out. In those circumstances, they will stop at nothing."

Under pressure

Meanwhile, George Bush, the US president, has called for an end to Mugabe's "tyranny" and urged African leaders who have not yet done so to "join the growing chorus" pushing for his ouster.
  
"As my administration has made clear, it is time for Robert Mugabe to go," Bush, who hands over to Barack Obama on January 20, said in a statement on Tuesday.

Bush's call followed tough action by the European Union which on Monday increased diplomatic pressure on the Zimbabwe government, broadening sanctions on Mugabe and his inner circle while Nicolas Sarkozy, the French president, added his voice to growing calls for Mugabe's resignation.

"We have a serious humanitarian crisis in Zimbabwe. We have cholera. Do they think that we can eradicate cholera with guns?"

Salva Rweyemamu,
the spokesman for Jakaya Kikwete,
the AU chairman and Tanzanian president

Raila Odinga, Kenya's prime minister, has also called on African nations to consider sending troops to Zimbabwe "to take control of the country and ensure urgent humanitarian assistance".

But the African Union has made it clear that it did not back calls for tougher action on Zimbabwe, saying only dialogue could solve the country's many problems and that sending in troops or removing Mugabe by force were not options.

"We have a serious humanitarian crisis in Zimbabwe. We have cholera. Do they think that we can eradicate cholera with guns?" said Salva Rweyemamu, the spokesman for Jakaya Kikwete, the AU chairman and Tanzanian president.

Doctors in Zimbabwe say the death toll could be much higher than the nearly 600 reported.

The UN children's agency Unicef said on Tuesday that it needed $17.5m to tackle the epidemic.

The disease has spread to neighbouring South Africa where a camp in Madimba on the border with Zimbabwe is accommodating hundreds of cholera-infected Zimbaweans seeking medical treatment.

Al Jazeera's Hoda Abdel-Hamid, reporting from the camp, said: "It is a huge problem because Zimbabweans keep pouring into South Africa. 

"Health authorities say that since November 15 they have registered about 630 cases here in South Africa. They say at the moment about 57 patients are in hospital and there have been eight deaths."

Caroline Hooper-Box from the aid organisation Oxfam told Al Jazeera that the situation in Zimbabwe is expected to get worse as the rain season is just about to start.

"The problem is that Zimbabwe's health and sanitation system is completely disintegrated. Cholera is a waterborne disease, and as the rain starts to fall, cholera spreads, further and faster. We're expecting things to become quite a lot worse, quite quickly," she said.

National emergency

Zimbabwe has declared a national emergency and appealed for international aid to fight the disease.

Basic foodstuffs in the country are running out, prices of goods are doubling every 24 hours, and the 100 million Zimbabwean dollar a week limit for bank withdrawals buys only three loaves of bread.

Nearly half the population is expected to need emergency aid next month, according to the United Nations.

Mugabe blames Western sanctions for Zimbabwe's crisis, while his critics accuse him of increasingly authoritarian rule.

The crisis has been accelerated by political deadlock between Mugabe and Morgan Tsvangirai, the opposition leader,  over implementation of a power-sharing deal brokered by South Africa.