The chief prosecutor of the International Criminal Court, Karim Khan, has been dismissed after a member states voted to remove him over allegations of sexual misconduct.

The 56-year-old British lawyer was relieved of his duties more than a year ago at his own request after members of his team, including a 39-year-old Malaysian lawyer, came forward with detailed claims of harassment.

Khan vigorously denied the allegations, but an internal investigation at the court, based in The Hague, concluded in June that he had committed a “serious breach of duty” by having a sexual relationship with a junior member of staff. He subsequently tried to pressure her into dropping her complaint, the inquiry found.

Supporters of Khan claimed he had been the victim of a smear campaign linked to his decision to issue arrest warrants for Israel’s prime minister Benjamin Netanyahu and former defence minister Yoav Gallant as part of an investigation into war crimes in Gaza.

It is the first time a prosecutor has been dismissed by the ICC in connection with a disciplinary investigation. Khan’s lawyer said he would challenge “the lawfulness and fairness of the decision”, but it is not clear what legal avenues are available.

The vote by a two-thirds majority of the ICC’s 125 members comes at a time when the court is coming under renewed pressure from the United States government.

US Secretary of State Marco Rubio claimed the court was a threat to American sovereignty and vowed to dismantle the institution “brick by brick”.

In an op-ed in the Wall Street Journal, Rubio claimed US border officials and elected leaders could be “dragged before an international court” and tried by foreign judges for the “so-called ‘crime’ of defending their own country.”

In fact, the ICC has no jurisdiction on US soil because the United States is not a member state.

In 2002 Congress passed the American Service-Members’ Protection Act (ASPA), nicknamed the Hague Invasion Act, which authorises the president to use “all means necessary and appropriate”, including military intervention, to release any American services personnel detained or imprisoned by the ICC.