Guinea's government has dispatched security forces to prevent RUSAL from exporting alumina from the port of Conakry, two sources with knowledge of RUSAL's operations said on Wednesday.

The measure was taken due to a row over alleged pollution caused by the firm's operations in the West African nation, the sources said.

RUSAL's Friguia refinery in Guinea has capacity for 640,000 tonnes of alumina a year which the Russian firm ships around the world for further refining into aluminium.

Our activities at the port have been halted. The environment ministry sent soldiers to surround the area and stop exports, a RUSAL employee who requested anonymity, told Reuters.

The source said Guinean authorities were reacting to alleged pollution caused by alumina leakage which they said could harm citizens not only at Fria where the Friguia refinery is based, 160 km from the capital Conakry, but also at the port.

Alumina is a derivative product of bauxite which further refined into aluminium metal. Guinea is the world's biggest supplier of the aluminium ore bauxite.

Another RUSAL official who requested not to be identified, confirmed the export block saying that the company was trying to stem the pollution.

In all alumina refineries across the world, there are emissions but at tolerable levels. We have discussed this with the authorities and we are trying to find a quick solution to the problem, he said.

Guinea environment ministry officials were not available for immmediate comment.