Former FBI director James Comey was indicted on Tuesday in an investigation over a social media photo of seashells arranged on a beach that officials said constituted a threat against US President Donald Trump, according to a person familiar with the matter.

The person was not authorised to publicly discuss the matter and confirmed the indictment on the condition of anonymity. The charge or charges against Comey were not immediately known.

It is the second criminal case the Justice Department has brought against the long-time Trump foe, who said he assumed the arrangement of shells he saw on a walk, reading “86 47”, was a political message, not a call to violence.

Comey is among multiple foes of the Republican president to come under scrutiny by the Justice Department over the last year, including as acting Attorney General Todd Blanche aims to position himself as the right person to hold the job permanently.

Comey was interviewed by the Secret Service in May after Trump administration officials asserted that he was advocating the assassination of Trump, the 47th president. Comey deleted the post shortly after it was made, saying: “I didn’t realize some folks associate those numbers with violence” and “I oppose violence of any kind so I took the post down.”

His lawyer did not immediately respond to a request seeking comment on Tuesday.