Iran has installed many more uranium enrichment machines in an underground bunker, diplomatic sources said on Thursday, potentially paving the way for a significant expansion of work the West fears is ultimately aimed at making nuclear bombs.Iran denies allegations it is seeking a nuclear weapons capability. But its refusal to curb its nuclear enrichment programme has prompted tough Western sanctions and has heightened speculation that Israel may attack its atomic sites.In a possible sign of further Iranian defiance in the face of such pressure, several sources said Iran had put in place additional enrichment centrifuges in its Fordow facility, buried deep inside a mountain to protect it against enemy strikes.