WASHINGTON (Reuters) - President Barack Obama will nominate former Republican Senator Chuck Hagel to be his defense secretary, and an announcement could come on Monday, a congressional Democratic aide said on Sunday.

The choice would likely set up a confirmation battle in the Senate over whether the former Nebraska senator strongly supports U.S. ally Israel. Hagel also has been criticized for comments he made on sanctions on Iran for its nuclear program.

(Reporting by Thomas Ferraro; Editing by Sandra Maler)