RIO Rio Tinto Plc

SYDNEY--Rio Tinto PLC (RIO) said it bought back more Australian stock than expected following a much-anticipated repurchase of shares here.

The Anglo-Australian mining company said its off-market tender of Rio Tinto Ltd. shares was increased to 560 million Australian dollars (US$426 million) from A$500 million due to strong demand.

Rio Tinto announced the buyback in February as part of a US$2 billion capital management program designed to bolster shareholder returns at a time when commodity prices have been falling. The price of A$48.44 a share was a discount of 14% to the market price.

Write to Rhiannon Hoyle at rhiannon.hoyle@wsj.com

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