Miners at four southwestern copper mines ended a six-day strike Thursday and returned to work after winning 30 percent pay increases plus higher bonuses, a Solidarity spokesman said.

In another development, Solidarity called on the Interior Ministry to investigate the planting of an eavesdropping device in one of its campaign offices after local officials refused to look into the matter.Preparatory work to reopen the mines began with the first shift, following the acceptance of the agreement by workers on Wednesday.