ROGERS -- The U.S. Secret Service is investigating a violent message aimed at Hillary Clinton written on the back of a minivan spotted on a highway northwest of Minneapolis.

The words on the van were photographed Wednesday by another person heading west on Interstate 94 near Rogers. The handwritten message contained profanities and said it wished that someone would shoot Clinton in the head if she won Tuesday's presidential race, which she lost to Republican Donald Trump.

Louis Stephens, special agent in charge of the Secret Service Minneapolis Division, says the agency is investigating.

Stephens says making threats against people protected by the Secret Service is a violation of federal law.

Rogers Police Chief Jeff Beahen says his department has been unable to reach the van's owner.