The FBI and Capitol Police are investigating a suspicious package containing white powder that was sent to Republican Sen. Rand Paul's home in Bowling Green, Kentucky, Monday Politico first reported.

Driving the news: Also in the large envelope was an image containing a death threat, Paul's spokesperson Sergio Gor confirmed in an email to Axios.

• Fox News obtained an image of the threat featuring Paul in bandages after his former neighbor Rene Boucher broke the senator's ribs in a 2017 attack.
• "I'll finish what your neighbor started you motherf--ker," the threat states.
• It's not yet known who sent the large envelope, but Paul tweeted that he takes "these threats immensely seriously."

What he's saying: "As a repeated target of violence, it is reprehensible that Twitter allows C-list celebrities to encourage violence against me and my family," Paul said in the Twitter post.

• He added in another tweet that he has been "targeted multiple times now."

Context: Paul noted in a statement to Politco, "Just this weekend Richard Marx called for violence against me and now we receive this powder filled letter."

• Marx tweeted Sunday: "If I ever meet Rand Paul's neighbor I'm going to hug him and buy him as many drinks as he can consume."
• Paul said in a Twitter post Monday night "it is reprehensible that Twitter allows C-list celebrities to advocate for violence against me and my family!"

What they're saying: A Twitter spokesperson declined to comment on Paul's remarks, but said in an emailed statement that a review found Marx's tweet was not in violation of the company's policies.

• Representatives for the FBI, Capitol Police and Marx did not immediately respond to Axios' requests for comment.

Editor's note: This article has been updated with new details throughout.