The US has imposed sanctions on senior officials in the International Criminal Court (ICC), including chief prosecutor Fatou Bensouda.
Secretary of State Mike Pompeo accused the court of “illegitimate attempts to subject Americans to its jurisdiction”.
The Hague-based ICC is currently investigating whether US forces committed war crimes in Afghanistan.
The US has criticised the court since its foundation and is one of a dozen states which have not signed up.
Created by a UN treaty in 2002, the court investigates and brings to justice those responsible for genocide, crimes against humanity and war crimes, intervening when national authorities cannot or will not prosecute.
The treaty has been ratified by 123 countries, including the UK. But the US – along with China, India and Russia – has refused to join, while some African nations have accused the body of being unfairly focused on Africans.
What are the sanctions?
President Donald Trump issued an executive order in June, which allows the US to block the assets of ICC employees and stop them entering the country.
Addressing reporters on Wednesday, Mr Pompeo said Ms Bensouda and Phakiso Mochochoko, the head of the Jurisdiction, Complementarity and Cooperation Division, were to be sanctioned under this order.
Dismissing the ICC as a “thoroughly broken and corrupted institution”, he said those who continued to “materially support those individuals risk exposure to sanctions as well”.
The US state department has also restricted the issuance of visas for ICC staff involved in “efforts to investigate US personnel”.
When President Trump issued his executive order in June, the ICC denounced what it called “further threats and coercive actions” against it.
“An attack on the ICC also represents an attack against the interests of victims of atrocity crimes, for many of whom the Court represents the last hope for justice,” its statement read.
What is the ICC investigating?
The ICC began investigating alleged war crimes committed by the US and others in the Afghan conflict earlier this year.
According to the ICC’s legal process, the court can issue arrest warrants or a summons to appear once prosecutors have gathered sufficient evidence and identified suspects. From there, they will decided if there is enough evidence for a case to go to trial.
At the time, Mr Pompeo vowed to protect Americans from the probe, calling it “a truly breathtaking action by an unaccountable, political institution masquerading as a legal body”.
A 2016 report from the ICC said there was a reasonable basis to believe the US military had committed torture at secret detention sites operated by the CIA.
The actions of the Taliban, the Afghan government and US troops since May 2003 are expected to be examined by the court.
Afghanistan is a member of the court but officials there have also expressed opposition to the inquiry.