Zimbabwean Prime Minister Morgan Tsvangirai said the number of cholera cases and deaths in his country is probably much higher than reported.

The World Health Organization said cholera has killed nearly 4,000 people and infected more than 87,000 others in Zimbabwe since August.

Addressing health workers Thursday, Mr. Tsvangirai said those figures are most likely a dramatic underestimate of the real figure.  He said many cases and deaths have gone unreported.

Zimbabwe is struggling with a general humanitarian crisis that includes the cholera epidemic, widespread food shortages, and a breakdown of the country's health care system.

Efforts to end the crisis have been hampered by economic and political turmoil in Zimbabwe.

On Wednesday, U.S. President Barack Obama said he is extending sanctions against Zimbabwean President Robert Mugabe and his allies.

In a notice to Congress, Mr. Obama said he is taking the action because Zimbabwe's political crisis has not been resolved.  

Mr. Mugabe and Mr. Tsvangirai joined forces in a power-sharing government last month under intense pressure from regional leaders.

The men and their parties continue to have strained relations over police arrests of human rights and opposition activists.  Some of the activists have been released in the last week.

The United States first imposed the sanctions nearly a decade ago in response to alleged human rights abuses by the Mugabe government.

Some information for this report was provided by AFP and Reuters.