Prosecutors in the Trump administration are accusing former FBI director James Comey of calling for violence against President Donald Trump by posting a photo online of sea shells assembled to draw out the numbers 8-6-4-7 on a beach.

Trump is the 47th American president, and the phrase "to 86" is a commonly-used restaurant industry term in American-English, meaning "to remove or eject". It is thought to have existed since the 1930s.

More recently, the term has taken on another lesser-known meaning - "to kill", according to Merriam-Webster, the oldest publisher of dictionaries in the US.

Comey deleted his post, and says he was unaware of the violent interpretation. Trump has disputed that, alleging that Comey was calling for his assassination "loud and clear".

This marks the second time the justice department has brought criminal charges against Comey, a longtime critic of Trump. In November, a judge dismissed charges that he lied to Congress during testimony and obstructed a congressional proceeding.