WASHINGTON (Reuters) - U.S. Senators Elizabeth Warren of Massachusetts and Tim Kaine of Virginia, and Julian Castro, the U.S. housing secretary, are on Democratic presidential candidate Hillary Clinton's short list of vice presidential picks, the Associated Press reported on Tuesday, citing Democratic sources.

U.S. Senator Bernie Sanders of Vermont, who waged a populist challenge to Clinton during an unexpectedly long primary campaign, was not on the list, the AP reported, citing one of several unidentified Democrats.

(Reporting by Washington newsroom; Editing by Jonathan Oatis)