Former US Secretary of State John Kerry has mocked President Donald Trump, saying he has the “immaturity of an 8-year-old boy and the insecurity of a teenage girl.”

Kerry made the remarks in an interview with HBO on Friday while discussing Trump’s frequent use of social media and touting former Trump campaign chairman Paul Manafort’s plea deal with the special counsel’s office.

On Friday, Manafort agreed to plead guilty to two criminal counts in Special Counsel Robert Mueller’s investigation.

According to court documents, Manafort pleaded guilty to one count of conspiracy against the country and one count of conspiracy to obstruct justice.

Kerry first praised Manafort’s plea deal and then launched into a personal attack on Trump.

“I don’t want to get into a real riff on this but I’ve got to tell you,” Kerry began.

“He really is the rare combination of an 8-year-old boy — he’s got the immaturity of an 8-year-old boy with the insecurity of a teenage girl,” he said.

Kerry also responded to Trump’s Twitter attack against him from the previous night when the president accused him of illegally meeting with foreign dignitaries after leaving the State Department.

“John Kerry had illegal meetings with the very hostile Iranian Regime, which can only serve to undercut our great work to the detriment of the American people. He told them to wait out the Trump Administration! Was he registered under the Foreign Agents Registration Act? BAD!” Trump tweeted on Thursday.