Striking staff have at times clashed with police

Owners of the Escondida site in Chile said talks with workers have been frozen, denying union claims of informal discussions.

Workers last week turned down an offer of up to $32,000 (�17,000) in bonuses and a 4% pay rise over three years.

The union is demanding bigger bonuses to reflect an upturn in profits.

But management at the mine, in which Anglo-Australian firm BHP Billiton has the majority stake, says it needs to protect itself against downturns in the copper price.

"The union says too many things," said mine spokesman Pedro Correa on reports that negotiations over pay and bonuses were continuing. "We are not talking."

The Escondida mine produces 8% of the world's copper.

Copper prices have hit record highs this year due to strong global demand led by China.