Mumbai: Rio Tinto, the world''s second-biggest mining company, is considering a counter offer to Alcoa Inc.''s $28.6-billion hostile bid for Alcan Inc., reports quoting sources close to the development said.

Rio has asked investment banks Credit Suisse and Deutsche Bank to advise it on a range of options, including a bid for Alcan and also a possible counter bid for Alcoa, though the bid actually materializing looked less likely.

Alcan is the world''s third-largest manufacturer of primary aluminum, behind Alcoa and Russia''s UC RUSAL and an Alcan-Rio combination would overtake RUSAL.

If Rio buys Alcan, it would have access to two of the world''s largest sources of bauxite - Rio ''s existing Weipa deposit and Alcan''s Gove deposit, both in Australia.

Earlier this week, Rio had announced plans to invest $1.8 billion in expanding its alumina refining operations, in which case, analysts pointed out, it would not bid for Alcan.

Alcoa, meanwhile, said the antitrust investigators of the US department of justice had sought additional information regarding its offer for Alcan. The company said it had a detailed road map to resolve competition issues through targeted divestitures and was looking to obtain approval by the end of this year.

"We continue to believe that a combination of Alcoa and Alcan makes strong strategic sense," Alcoa chief executive Alain Belda said.

Alcoa made its bid on 7 May, after the collapse of two years of merger talks with Alcan. Alcan, meanwhile has others possible suitors, including BHP Billiton Ltd. Plc., Norsk Hydro ASA, Companhia Vale do Rio Doce, RUSAL, Anglo American and Xstrata Plc. are also viewed by analysts as potential bidders for Alcan.

Alcan, which split off from Alcoa in the 1920s because of antitrust regulations, is expected to unveil its own strategy in the coming weeks, which will indicate whether it wants to remain independent, find another suitor or reach a friendly deal with Alcoa.