March 30 (Reuters) - Belarus will allow companies to export potash fertiliser in response to Western sanctions, starting on April 6, RIA news agency said on Wednesday, citing a government decision.

Belarus is the world's third-largest producer of the crop nutrient after Canada and Russia and state-owned Belaruskali is one of the world's largest players.

RIA said the Belarus government would grant export licenses to Belaruskali and the Belarus Potash Co (BPC). Washington has given BPC clients until April 1 to wind down their business with the firm.

This month, the European Union tightened existing sanctions on Belarus to completely ban potash exports while conceding they could still be sent to Russia or third countries.

Landlocked Belarus previously relied on shipments from the Baltic Sea port of Klaipeda in Lithuania. Vilnius halted the use of its railway for Belarus exports from Feb. 1.

Belarusian President Alexander Lukashenko said on March 21 that the potash market would need to be discreet, like the arms trade, a local agency reported. (Reporting by David Ljunggren; Editing by Leslie Adler and David Gregorio)