Among other companies sources previously said have shown interest in Alcan are Brazil's CVRD.
Alcan, which has long said it was in talks with third parties as part of efforts to fight off Alcoa , switched gears slightly this week in describing those negotiations.
It now says it has signed confidentiality and standstill agreements with those parties, indicating the company has moved further along in the negotiating process.
But Alcan declined to name the third parties, or say who it was talking to.
"We're in negotiations with third parties," said spokeswoman Anik Michaud.
A Rio spokesman in London had no comment. The company has at least two investment banks -- Deutsche Bank and Credit Suisse Group -- working for it, sources have said. According to Canada's Globe and Mail newspaper, it recently hired CIBC World Markets as well. CIBC said it had no comment.
BHP, which has hired Merrill Lynch, according to sources, also declined to comment.
One issue that any rival bid must consider is that, under its agreements on power supply and waterways rights with Quebec province, Alcan must keep its head office in Montreal.
Alcan shares rose $1.71 cents to $87.85 on the New York Stock Exchange and rose C$2.55 to C$92.75 on the Toronto Stock Exchange in early afternoon trading. Alcoa shares rose 54 cents to $42.21 in New York.
Alcan has repeatedly rejected Alcoa's May 7 offer as inadequate.
Based on Alcoa's most recent share price on the New York Stock Exchange, its offer valued Alcan at $75.94 a share.
Alcan has declined to enter talks with Alcoa, in part because it says Alcoa refused to sign a confidentiality and standstill agreement during friendly talks that collapsed last year.
Alcoa this week extended its $28.6 billion offer for Alcan to Aug. 10. It also signed a $30 billion line of credit from Goldman Sachs Group and Citigroup, which are advising it on the offer.