The Commission has expressed worries about reduced competition and higher prices as a result of the deal, with carmakers in particular feeling the impact.

The EU competition enforcer did not provide details of the concessions, in line with its policy. It is expected to seek feedback from rivals and customers before deciding by Oct. 7 whether to clear the bid.

Novelis, part of India's Hindalco Industries ran the risk of seeing the deal blocked if it did not offer concessions, sources close to the matter told Reuters earlier this month.

The company could make a written commitment to boost capacity and add 80 new jobs at the Aleris plant in Duffel, Belgium, to allay regulatory concerns that capacity may be curtailed to increase prices, the people said.

Novelis said it was working constructively with the Commission.

"While we have no definitive information to share at this time, we are exploring a range of options, including potential remedies, with the continued aim of closing the transaction by the end of this calendar year," Novelis said in a statement.

(Reporting by Foo Yun Chee; Editing by Susan Fenton and Jan Harvey)

By Foo Yun Chee