WASHINGTON, Sept. 2 (AFP) - US Secretary of State Mike Pompeo on Wednesday (Sep 2) slapped sanctions on the top prosecutor of the International Criminal Court - a move that The Hague-based tribunal called a "serious" attack against the rule of law.

The economic sanctions against Fatou Bensouda and another senior ICC official, Phakiso Mochochoko, after earlier visa bans on Bensouda and others failed to head off the court's war crimes probe into US military personnel in Afghanistan.

"Today we take the next step, because the ICC continues to target Americans, sadly," Pompeo said.

The ICC quickly fired back.

"These coercive acts, directed at an international judicial institution and its civil servants, are unprecedented and constitute serious attacks against the court, the Rome Statute system of international criminal justice, and the rule of law more generally," it said in a statement.

The sanctions freeze the US assets of the two officials, and bar any US individuals from doing business with them.

'KANGAROO COURT'

President Donald Trump had authorised sanctions on the ICC on Jun 11 over its investigation of US troops.

Pompeo at the time referred to the ICC as a "kangaroo court" and warned that if US soldiers were targeted, those of US allies in Afghanistan risked the same treatment.

Despite the new sanctions, the ICC appeared to give no ground on the issue, saying it "continues to stand firmly by its personnel and its mission of fighting impunity for the world's most serious crimes."

And the head of the ICC's Assembly of States Parties, O-Gon Kwon, said the oversight body would meet to discuss how to support the tribunal in the face of the US measures.

The US measures "only serve to weaken our common endeavour to fight impunity for mass atrocities," Kwon said.

CHALLENGE TO COURT'S LEGITIMACY

The sanctions were announced just two months before US elections, in which Trump is running for re-election in part on his record of standing up to international institutions that don't bow to US demands.

But Washington's move also added to the broader pressure on the ICC to shore up its legitimacy, 18 years after it was founded to prosecute war crimes, crimes against humanity and genocide.

The United States - like Russia, China, Israel, Syria and a number of other countries - is not a member of the ICC, and its opposition to the court is longstanding.

In 2002, the US Congress even passed the so-called "Hague Invasion Act" allowing the US president to authorise military force to free any US personnel held by the ICC, in theory making an invasion of Dutch shores a possibility.

'NEW LOW'

But the investigation into alleged wartime atrocities in Afghanistan possibly involving US military and civilian officials has turned Washington's low-level opposition into a concerted campaign against the institution.

The United States argues that it has its own procedures in place to investigate accusations against troops.

Trump, however, used his executive powers last year to clear three military members over war crimes, including in Afghanistan.

Also underpinning Washington's enmity is the ICC's investigation into alleged war crimes by US ally Israel against Palestinians in the West Bank and Gaza.

Last year the Trump administration revoked Bensouda's US visa, but the court has continued with the probe, leading to the president's June decision to permit economic sanctions against the court.

Dutch Foreign Minister Stef Blok said his country was disappointed over the US move.

The Netherlands "will continue to support the ICC's independence and functioning in its fight against impunity. With our EU partners we'll look at how we can best support the Court," he said in a tweet.

Balkees Jarrah, senior counsel at Human Rights Watch, said the sanctions move "marks a shameful new low for US commitments to justice for victims of the worst crimes."