THE HAGUE (Reuters) - The prosecutor of the International Criminal Court on Friday said she would seek approval to open a formal investigation into allegations of war crimes in Afghanistan, in a case that could examine the role of U.S. forces abroad.

Fatou Bensouda said in a statement that there is a “reasonable basis to believe” war crimes and crimes against humanity were committed and that all sides in the conflict would be examined.

The prosecutor will focus on crimes allegedly committed since May 2003 on the territory of Afghanistan, and war crimes closely linked to the situation in Afghanistan allegedly committed since July 2002 on the territory of other states.

The prosecutor on Friday did not mention any specific parties to be investigated.

In a report last year, ICC prosecutors identified “potential cases” among three groups of alleged perpetrators: the Taliban and its affiliates, the Afghan authorities and members of the U.S. armed forces and Central Intelligence Agency.

There were preliminary grounds to believe U.S. forces committed war crimes in Afghanistan and at CIA detention facilities elsewhere in 2003 and 2004, it said.

The alleged atrocities took place in all 34 of Afghanistan’s provinces, with a smaller number of crimes alleged in Poland, Lithuania and Romania, where suspected members of the Taliban or Al Qaeda were held for questioning.

If authorized by the court’s judges, prosecutors will investigate “in an independent, impartial and objective way, crimes within the court’s jurisdiction allegedly committed by any party to the armed conflict.”

ULTIMATE FOCUS ON MOST SERIOUS CRIMES

“The ultimate focus will be upon those most responsible for the most serious crimes,” she said in the statement.

The ICC was established in 2002 as the world’s permanent court for prosecuting the most serious war crimes, including genocide.

It has the backing of the European Union and dozens of nations, but several of the world’s most powerful countries - notably the United States, Russia and China - never joined.

Former U.S. administrations first opposed the court’s establishment, citing fears that American service members would be targeted by politically-motivated prosecutions, but later backed ad hoc investigations.

A court of last resort, the ICC only steps in when a country’s government is found to be unwilling or unable to do so. ICC jurisdiction is limited to crimes committed on the territory of member states, or in cases referred to it by the U.N. Security Council, as happened with Sudan over alleged genocide in Darfur in 2005.

However, crimes committed on the soil of member states by soldiers of countries who are not members also fall under the court’s jurisdiction under international law.

If a state can show it has investigated and prosecuted the same crimes the ICC is looking into, it could avoid any case ending up in The Hague.

In a 2016 report on the preliminary examination of alleged crimes in Afghanistan, the prosecutor noted that while the U.S. Dept. of Justice has looked into allegations of ill treatment of CIA detainees in 2009-2011, the scope of the probe was limited and two cases did not result in a prosecution.