Washington DC - Homeland Security Secretary Kristi Noem said ex-FBI director James Comey is being investigated for allegedly making an assassination threat against President Donald Trump.

The announcement by Noem came after Comey made a now-deleted post on Instagram that showed an image of "86 47" spelled out in seashells, with "86" being slang for getting rid of something or someone, and Trump being the 47th president.

"Disgraced former FBI Director James Comey just called for the assassination of @POTUS Trump," Noem posted on X.

"DHS and Secret Service is investigating this threat and will respond appropriately," she said.

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Comey later said on Instagram that he posted "a picture of some shells I saw today on a beach walk, which I assumed were a political message."

"I didn't realize some folks associate those numbers with violence. It never occurred to me but I oppose violence of any kind so I took the post down," he wrote.

Trump was wounded in the ear during an assassination attempt that took place while he was holding a rally in Butler, Pennsylvania in July, and has faced other threats.

"He knew exactly what that meant. A child knows what that meant. If you're the FBI director and you don't know what that meant, that meant assassination," the president said of Comey's post in an interview with Fox News.