CONAKRY, May 26 (Reuters) - Workers at Russian aluminum giant Rusal's Guinea bauxite mine Compagnie des Bauxites de Dian Dian went on strike on Thursday, a union leader told Reuters, in a move Rusal said was illegal.

A worker told Reuters production at COBAD had stopped due to the strike. Rusal did not respond to a request for comment on whether production was continuing. "All we can say is that the strike is illegal," a Rusal spokesperson said, declining to detail the reasons why.

The workers at COBAD are demanding better working conditions and a salary increase, union leader Yamoussa Bangoura said by telephone, adding that COBAD was given notice of a strike on May 7.

"We have asked everyone to stop working until our demands are met," Bangoura said. Workers decided to strike after talks with COBAD management on Wednesday were inconclusive, he said.

Guinea is the world's second-largest producer of bauxite, an ore used to make aluminum, and a key supplier of bauxite to China. It produced 83 million tonnes of bauxite in 2021, Guinea's mines ministry statistics showed.

COBAD produced 3.59 million tonnes of bauxite last year, while Rusal's other Guinea operation, Compagnie des Bauxites de Kindia, produced 2.65 million tonnes, according to the mines ministry.

COBAD stopped exporting bauxite from Guinea for nearly a month in March as Russia's invasion of Ukraine disrupted Rusal's supply chains. (Reporting by Saliou Samb in Conakry; Additional reporting by Helen Reid in Johannesburg; Editing by Mark Potter and David Evans)