WASHINGTON - John Bolton, who served as the US national security adviser during US President Donald Trump's first term from 2018 to 2019, was indicted on Thursday, marking the third indictment of high-profile Trump foes in less than a month.

Bolton, who was indicted by a federal grand jury in the US District Court in the District of Maryland, faces 18 charges, including eight counts of transmission of national defense information and 10 counts of retention of national defense information.

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The federal grand jury charged Bolton with "serious crimes related to the mishandling of classified information," the US Justice Department said in a statement.

"Like many public officials throughout history, Ambassador Bolton kept diaries -- that is not a crime. We look forward to proving once again that Ambassador Bolton did not unlawfully share or store any information," Bolton's lawyer Abbe Lowell was quoted by CNN as saying in a statement.

In a statement, Bolton said that he is a target of Trump's retribution campaign against his perceived political opponents.

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When asked about the indictment, Trump told reporters in the White House, "I think he's a bad person."

Earlier this year, FBI agents executed search warrants at Bolton's residence in Maryland and his office in Washington, D.C., seizing numerous documents marked "classified," "secret" and "confidential," according to court records.

The latest indictment came less than a month after former FBI Director James Comey and New York Attorney General Letitia James were successively indicted in the US District Court for the Eastern District of Virginia.

Bolton has been a vocal critic of the president since leaving the administration, describing Trump as "unfit to be president."