A leader of the Rwandan FDLR rebel group has been arrested in France on war crimes charges, the International Criminal Court says.
In a sealed warrant, Callixte Mbarushimana is accused of 11 counts of murder, rape and other crimes committed during the long conflict in DR Congo.
He last year told the BBC he denied any responsibility for war crimes and said FDLR fighters did not attack civilians.
FDLR fighters were recently accused of raping hundreds of people in DR Congo.
Again, the mainly Hutu FDLR (Democratic Forces for the Liberation of Rwanda) denied links to the attacks around the eastern Congolese town of Luvungi.
Some FDLR leaders have been accused of taking part in the 1994 genocide of ethnic Tutsis and moderate Hutus in Rwanda.
After a Tutsi-dominated group took power in Rwanda, they fled into what is now the Democratic Republic of Congo, sparking years of unrest in the region.
The ICC said that as executive secretary of the FDLR, Mr Mbarushimana was criminally responsible for five counts of crimes against humanity and six counts of war crimes committed throughout 2009.
In a statement, the court said Mr Mbarushimana had "personally and intentionally contributed to a common plan of conducting attacks against the civilian population" with the aim of creating a "humanitarian catastrophe".
ICC Prosecutor Luis Moreno-Ocampo said Mr Mbarushimana's arrest was "a good day for justice" and marked a "crucial step in efforts to prosecute the massive sexual crimes committed in the DRC".
But he warned there was "still a lot to do to break the cycle of impunity in the DRC" with 15,000 cases of sexual violence reported in 2009.
"Another commander sought by the ICC for massive crimes, Bosco Ntaganda, is still at large in Goma and his forces roam the Kivus killing and raping. He must be next," said Mr Moreno-Ocampo.
The FDLR is one of the most powerful rebel forces operating in eastern DR Congo, where they are believed to make millions of dollars a year by controlling mines rich in gold and other minerals, and extorting money from local people.
Mr Mbarushimana, who has been living in Paris, has described the force as a freedom movement, fighting "to liberate the Rwandan people from the yoke of the fascist regime" of the governing Rwandan Patriotic Front (RPF).
He has always said he is innocent but that he is "ready to face justice if they come with allegations".
Lambert Mende, a spokesman for the Congolese government, welcomed Mr Mbarushimana's arrest.
"It's good news for the Democratic Republic of Congo and the whole Great Lakes region as Mbarushimana led from Europe the FDLR's armed bands which spread death and destruction in our country and threatened security in their own country," he told the AFP news agency.
Rwanda has twice sent its troops into DR Congo, saying they are needed to stop Hutu fighters, such as the FDLR, from using Congolese territory to attack Rwanda.
This led to the six-year conflict in DR Congo and the deaths of some five million people.