Alcan Inc., the big Canadian aluminum maker, said on Friday that a US$28.6-billion hostile takeover offer from American rival Alcoa remains inadequate, and that it is pursuing alternatives such as talks with other groups.

Alcan spokeswoman Anik Michaud declined to comment on reports that Rio Tinto, the world's second-largest miner, has asked investment banks to advise it on options, including a possible counterbid for Alcan.

"We've said that from the outset that we were in discussion with third parties," Michaud said.

She declined to identify the third parties.

Earlier on Friday, Alcoa said U.S. Department of Justice antitrust investigators had asked it for additional information regarding its May 7 offer for Alcan.

Alcoa said it had a detailed road map to resolve competition issues.

Alcan's Michaud said she expects Alcoa to extend the July 10 deadline on its offer.

"We contend that from the beginning, Alcoa has underestimated the substantive impediments to achieving the regulatory clearances," Michaud said.

She added that Montreal-based Alcan is not bound by any timing considerations at this point on unveiling its strategy to counter the Alcoa offer.

Alcan shares were up $1.13 at US$86.23 on the New York Stock Exchange on Friday morning and up 59 Canadian cents at C$90.41 on the Toronto Stock Exchange.