Brazilian miner Vale has raised its bid for rival Xstrata by 17 percent to more than $89 billion, and a formal offer is expected in the coming days, a source with direct knowledge of the merger talks said Thursday.

The source, who asked to be unnamed, said the company has raised its bid to 47 pounds a share from 40 pounds. Xstrata, an Anglo-Swiss miner, declined to comment on the matter.