Former FBI director James Comey has been interviewed by the US Secret Service regarding a social media post on Instagram that featured a photo of seashells spelling out the numbers '8647'.

The post, which was later deleted, sparked controversy among Republicans who claimed it was an incitement to violence against President Donald Trump.

The number '86' is a slang term with multiple definitions, including 'to reject' or 'to get rid of', but has also been used to mean 'kill'.

Trump is the 47th US president.

Comey participated in the questioning voluntarily at the Secret Service's Washington DC headquarters and was not taken into custody.

The interview lasted approximately an hour.

President Trump stated earlier that Comey's post was a call for his assassination, saying 'a child knows what that meant' and that it 'says it loud and clear'.

Trump added that any decision on whether to file charges against Comey would be up to the Attorney General.

Comey posted the photo on Thursday and then deleted it amid conservative backlash, later stating that he had seen the shells during a walk on the beach and assumed they were a political message, but did not realize some people associated those numbers with violence.

Homeland Security Secretary Kristi Noem announced on social media that the Secret Service had interviewed Comey regarding the post, which she described as 'calling for the assassination of President Trump'.

The Director of National Intelligence has also commented on the matter, calling for Comey to be jailed for allegedly 'issuing a hit' on the president.