Heavy flooding after torrential rains has affected more than 130,000 people in seven West African countries, with impoverished Burkina Faso, Mali and Mauritanian worst hit, the United Nations said on Saturday.

More than 30,000 people have been stricken in both Mali and Mauritania, with some 20,000 affected in landlocked Burkina Faso since the flooding began in July, the U.N. Office for Coordination of Humanitarian Affairs (OCHA) said on its Web site.

Niger, Gambia, Senegal and war-shattered Liberia have also been struck by the flooding.

Floods have destroyed houses, food stocks and goods, and polluted water sources, leaving tens of thousands of people homeless and vulnerable to water-borne diseases such as cholera.

So far, only the government of Mauritania has appealed for international aid, while in Mali and Niger the authorities have requested assistance from their local U.N. teams, OCHA said.

In Mauritania, where civil defence officials said some 30,000 people had been affected in the southeastern city of Tintan, heavy rains have hit neighbouring settlements in recent days.

In the town of Barkeol, more than a hundred houses have been destroyed in the past three days by the deluge.

"We are isolated because all the roads into the area have become impassable," said regional prefect Hacen Ould Ahmed. "The population of Barkeol is threatened."

The disaster comes during the annual lean season in the normally-arid Sahel belt, south of the Sahara, when many households already face difficulties finding food. Having to shelter flood victims could place an intolerable strain on already scarce resources.

West Africa is home to some of the world's least developed and poorest countries.