Canadian auto parts group Magna and its Russian partner Sberbank improved their offer for carmaker Opel at the last minute to seal a deal with General Motors, a source close to the negotiations told Reuters.

The source said a GM board meeting next week could formalize the decision on the winning Opel bidder.

Magna was battling Belgium-based investor RHJ International for control of the venerable German-based carmaker.

(Reporting by Gernot Heller; Writing by Noah Barkin)