The head of a Rwandan rebel group accused of committing war crimes in Democratic Republic of Congo has been extradited from France to The Hague.
Callixte Mbarushimana was arrested in Paris last October, following a request from the International Criminal Court.
The Hutu rebel leader has denied accusations that he ordered his FDLR fighters to kill and rape civilians.
The move came as the FDLR was accused of attacking a wildlife patrol.
The director of Virunga National Park in eastern DR Congo said three rangers and five government soldiers died in the rocket-propelled grenade attack on their vehicle.
Emmanuel de Merode said more than 130 park rangers have died since 1996 when the conflict began in the volatile east.
The presence in DR Congo of Hutu rebels has been at the heart of years of unrest in the region.
Mr Mbarushimana, 47, faces five counts of crimes against humanity and six counts of war crimes, including charges of murder, torture, rape, inhumane acts and persecution, and destruction of property.
A French court has previously rejected an appeal against Mr Mbarushimana's extradition but ruled he should not be sent to Rwanda, where his lawyers say he would not get a fair trial.
ICC chief prosecutor Luis Moreno-Ocampo said the prosecution of the FDLR leaders "will provide the opportunity to demobilise this armed group".
"Rape can no longer be used as a weapon of war. In the ICC era, the fate of leaders and commanders who plan or oversee campaigns of mass crimes against civilians is to face justice," he said.
Mr de Merode said he had had reports in recent days of more than 700 FDLR fighters coming into Virunga park territory.
The park, in North Kivu province, is home to some of the world's last remaining mountain gorillas and is managed by the Congolese Institute for the Conservation of Nature (ICCN).
"They are extremely hostile towards ICCN ever since we started to stop the forest destruction for charcoal, an illegal industry from which they were making significant revenue," he said in a statement.
He said the attackers escaped by foot and that it was the worst attack in the park in the last 12 months.
FDLR fighters were accused of raping hundreds of people in eastern DR Congo last year, although the group has denied responsibility.
Some FDLR leaders allegedly took part in the 1994 slaughter of some 800,000 ethnic Tutsis and moderate Hutus in Rwanda.
After a Tutsi-dominated group took power ending the genocide, some FDLR members fled into what is now DR Congo, sparking years of unrest in the region.
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.
The FDLR is now one of the most powerful rebel forces operating in the east of the country, 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 FDLR as a freedom movement, fighting "to liberate the Rwandan people from the yoke of the fascist regime" of the Rwandan Patriotic Front (RPF), which is still in power in Kigali.