BERLIN (AP) — Two Syrian men have been arrested in Germany on suspicion of membership in extremist groups, and one of them is suspected of involvement in a 2013 attack in eastern Syria in which more than 60 Shiite fighters and civilians were killed, prosecutors said Thursday.

The suspects, identified only as Amer A. and Basel O. in line with German privacy rules, were arrested on Wednesday, the federal prosecutors’ office said. Both are accused of membership in a foreign terrorist organization — Liwa Jund al Rahman, or Brigade of the Soldiers of the Merciful God, an armed rebel group that prosecutors said Amer A. formed in February 2013 and led.

Amer A. is also accused of committing war crimes by means of forced displacement and of membership in the Islamic State group.

The war crimes charges relate to a June 2013 attack on Hatla, in Syria’s eastern Deir el-Zour province, that killed about 60 Shiite residents. At the time, the attack underlined the increasingly sectarian nature of Syria’s civil war. Prosecutors said the attack was carried out jointly by Liwa Jund al Rahman under Amer A.'s command and other jihadi groups.

Survivors of the attack were forced to flee to elsewhere in Syria or abroad “by intentionally stoking fears of death — also by means of arson and looting,” prosecutors said in a statement. “This forced displacement meant the end of all Shiite presence in Hatla.”

Amer A. joined IS in July 2014 and put his group under its command, prosecutors said. They said Basel O. took a “prominent military position” in his group by late 2013 and commanded units of the organization in battles with Syrian government forces in December that year and in April 2014, particularly at Deir el-Zour’s military airfield.

A judge on Wednesday ordered the two suspects held in custody pending a potential indictment.

Germany’s application of the rule of “universal jurisdiction,” allowing the prosecution of serious crimes committed abroad, led last year to the first conviction of a senior Syrian official for crimes against humanity.

And in February, a German court convicted a Palestinian man from Syria of a war crime and murder for launching a grenade into a crowd of civilians waiting for food in Damascus in 2014.