US President Donald Trump suggested on Wednesday that people in the state of North Carolina should vote twice in the November election, once in person and once by mail, although doing so is a crime.

“Let them send it in and let them go vote,” Trump said in an interview with WECT-TV in Wilmington, North Carolina, when asked about the security of mail-in votes. “And if the system is as good as they say it is then obviously they won’t be able to vote” in person.

Voting more than once in an election is illegal.

“President Trump outrageously encouraged” North Carolinians “to break the law in order to help him sow chaos in our election”. state attorney-general Josh Stein said in a tweet. “Make sure you vote, but do NOT vote twice! I will do everything in my power to make sure the will of the people is upheld in November.”

US attorney-general William Barr told CNN that Trump “was trying to make the point that the ability to monitor this system is not good”. Told that voting twice is illegal, he said,

“I don't know what the law in the particular state says.”

Barr said mail-in ballots for the November 3 election could be vulnerable to fraud, echoing an argument Trump has made to denounce the use of voting by mail.

Trump has previously said the voting method is susceptible to large-scale fraud, although experts say voter fraud of any kind is extremely rare in the US.

Voting by mail is not new in the United States — nearly one in four voters cast presidential ballots in 2016 that way.