A dearth of rainfall in the Sahel could have "severe consequences" for food and agriculture across the region, a UN official said Tuesday, urging urgent action to tackle droughts.

"The countries in the Sahel in general are suffering from a lack of rain this winter, the consequences of which could be severe," Coumba Mar Gadio, Mauritania's UN representative, warned at a meeting of regional environment ministers in Nouakchott.

"Most of the rural populations (in the region) are dependent on the rains" for food and work, she said, adding that it was "urgent to put in place sustainable methods of production and consumption."

The Sahel, which stretches from Mauritania in the west to Eritrea in the east, has undergone three major droughts in less than a decade and has seen huge swathes of land turn to desert.

The UN is backing a regional plan to build a "Great Green Wall" of trees and vegetation which aims to stop the advance of the sands and lessen the effects of desertification.

Many countries in the region are already experiencing a delay in their rainy seasons, and the UN representative said the initiative aimed to strengthen the resilience of countries and communities in the face of climate change.

The green wall will be around 15 kilometres (9 miles) wide and stretch over more than 7,000 kilometres from Senegal in the west to Djibouti in the east.

Experts estimate that Africa has lost around 650,000 square kilometres of productive land in the last 50 years, an area greater than the size of France.