Anglo American rejected BHP’s $60 billion takeover bid on Friday after concluding it “significantly undervalues” the target, forcing BHP to consider sweetening its offer or walk away from its global copper dream.

“The BHP proposal is opportunistic and fails to value Anglo American’s prospects, while significantly diluting the relative value upside participation of Anglo American’s shareholders relative to BHP’s shareholders,” said its chairman, Stuart Chambers, in a statement to the London Stock Exchange.