German authorities have arrested a Libyan war crimes suspect accused of being a senior official at a notorious prison where inmates were routinely tortured and sometimes sexually abused, the International Criminal Court said on Friday.

Khaled Mohamed Ali Al Hishri, alleged to have been a member of the Special Deterrence Force armed group during Libya's civil war, was arrested on Wednesday, German authorities said.

The ICC said he would remain in German custody, pending the completion of national proceedings.

Prosecutors at the ICC accuse Al Hishri of war crimes and crimes against humanity, including murder, torture and rape from February 2015 until early 2020, a period during which he was allegedly one of the most senior officials in the Mitiga prison.

According to the prosecution, Mitiga was the largest detention facility in western Libya, where thousands of detainees were held in cramped cells without basic hygiene and were systematically subjected to brutal interrogations and torture.

Men and women held there also faced sexual violence including rape, the prosecution said.

It is a critical time for the ICC. Its prosecutor and four judges are facing U.S. sanctions in retaliation for an arrest warrant it issued for Israeli Prime Minister Benjamin Netanyahu for alleged war crimes and crimes against humanity in the Gaza conflict. A number of European ICC member states, including Germany, have also criticised the warrant.

In addition to the sanctions, the ICC is also operating without its chief prosecutor Karim Khan, who stepped aside temporarily two months ago as he faced a probe by United Nations investigators into alleged sexual misconduct.

Khan denies the allegations, and his two deputy prosecutors are running the office in his absence.

In a statement on Friday, the office of the prosecutor said it expected Al Hishri to be transferred to The Hague and added that it stood ready to start his trial.

"This development is so needed at a time of unprecedented turmoil in the field of accountability generally and at the ICC specifically," Kip Hale, an attorney who documented crimes in Libya for the UN, told Reuters.

"Yet, it is most important for the victims of the many atrocity crimes committed at Mitiga prison," he added.

Italy arrested another Libyan ICC suspect, Osama Elmasry Njeem, in January but subsequently returned him to Tripoli, saying the arrest warrant contained mistakes and inaccuracies. He was also accused of crimes committed against detainees in Mitiga prison.

His release sparked outrage among Italian opposition parties and triggered a legal investigation into Prime Minister Giorgia Meloni and several other government members.

The court has been investigating allegations of serious crimes committed in Libya since the outbreak of its civil war in 2011, following a referral by the UN Security Council.