French authorities Monday arrested Callixte Mbarushimana, the executive secretary of the Democratic Force for the Liberation of Rwanda, known by its French initials FDLR.
The International Criminal Court in The Hague wants the rebel leader for war crimes and crimes against humanity, including torture, rape and murder.
The FDLR was fingered in the gang rape of hundreds of women in the region during the summer.
Geraldine Mattioli-Zeltner, a justice advocate for Human Rights Watch, said the arrest of the FDLR leader sends a strong message to rebel forces in the region.
"Many forces in eastern Congo have committed grave crimes against civilians, making it crucial for the ICC prosecutor to promptly investigate and, as appropriate, bring charges against their leaders," she said in a statement. "Leaders of the Congolese army and rebel commanders need to feel they will no longer get away with murder."
Human Rights Watch adds the FDLR is linked to "widespread and vicious attacks" against civilians in response to U.N.-backed military operations launched in the area in 2009.
The U.N. Security Council was called on to consider targeted sanctions against the FDLR and the Congolese Mai Mai militia for their role in the mass rapes.