Washington (CNN) The United States Secret Service has been alerted in response to a tweet by actor Peter Fonda, who said Barron Trump -- President Donald Trump's youngest son -- should be separated from his mother and put "in a cage with pedophiles."

"We should rip Barron Trump from his mother's arms and put him in a cage with pedophiles and see if mother will will stand up against the giant a--hole she is married to. 90 million people in the streets on the same weekend in the country. F---," Fonda wrote in a tweet, which has since been deleted.

First lady Melania Trump's communications director, Stephanie Grisham, called the tweet "sick and irresponsible," adding that the Secret Service has been notified. A Secret Service spokesman said the agency is aware of the tweet but declined to comment, citing the agency's practice of not speaking about protective matters.

The President's eldest son, Donald Trump Jr., weighed in on Twitter as well.

"You're clearly a sick individual and everyone is an internet bada-- but rather than attack an 11 year old like a bully and a coward why don't you pick on someone a bit bigger. LMK," Trump Jr. tweeted, using the shorthand Internet term for "let me know."

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