RHJ International SA, a Belgian investment firm, plans to sweeten its bid for General Motors Co's European unit to overcome German government opposition to its bid, The Wall Street Journal said on Friday.

The firm is proposing to lower the amount of needed German taxpayer-funded loan guarantees to support a purchase of the Opel and Vauxhall operations to as little as 3.6 billion euros ($5.11 billion) from 3.8 billion euros ($5.39 billion), the newspaper said, citing people familiar with the matter.

The lower amount would be 900 million euros below the aid envisioned in a rival offer by Magna International Inc, the newspaper said.

RHJ and GM did not immediately return requests for comment.

(Reporting by Jonathan Stempel)