John Bolton, Donald Trump's former national security adviser, has pleaded not guilty to charges of mishandling classified information.

The 18 charges stem from allegations he shared or retained sensitive materials, including some characterized as top secret. He entered the plea after surrendering to authorities at a federal court hearing on Friday.

Bolton served during Trump's first administration but parted with the White House contentiously, and has become one of the president's most vocal public critics.

The indictment makes Bolton, 76, the third of the US president's political opponents to face charges in recent weeks. Bolton has said he would defend his lawful conduct.

Bolton, wearing a dark blue suit and maroon tie, did not speak with reporters as he arrived at the courthouse in Greenbelt, Maryland.

Prosecutors accuse Bolton of using personal messaging apps and email to illegally transmit sensitive information.

These documents revealed intelligence about future attacks, foreign adversaries, and foreign-policy relations, the prosecutors wrote.

Bolton expressed that he had become the latest target in weaponizing the Justice Department to charge those he [Trump] deems to be his enemies with charges that were declined before or distort the facts.

The charges also allege that between 2019 and 2021, Bolton was targeted by a hacking attack associated with Iran, which gained access to his account, exposing classified materials.

His attorney, Abbe Lowell, argued that the documents in question were unclassified, only shared with family, and known to the FBI since 2021.

The Justice Department's investigation into Bolton continued into the Biden administration, but initially did not result in charges.

In 2020, the department tried to block Bolton's book release over concerns it contained classified information, although a federal judge eventually ruled against the government's attempt.

The indictment raises significant concerns about the handling of sensitive materials amongst prominent political figures and highlights ongoing tensions within the landscape of U.S. politics.