UN peacekeepers and the army in the Democratic Republic of Congo have arrested a rebel leader suspected of leading attacks involving mass rape.
The UN said Lt Col Mayele of the Mai Mai Cheka rebel group was captured in a joint operation in North Kivu province.
Between 300 and 500 people are thought to have been raped during violence in eastern DR Congo in July and August.
Peacekeepers were criticised for failing to stop the attacks, some of which took place close to a UN base.
A UN spokesman said Lt Col Mayele, who was arrested in the province's Walikale region, was in custody at a Congolese military court in the provincial capital, Goma.
A deputy in the Mai Mai militia, he was handed over by the group's leader, named as Cheka, UN officials said.
It is unclear why Cheka turned against Lt Col Mayele, says the BBC's Thomas Fessy in Kinshasa.
The arrest was carried out while the UN's representative on sexual violence, Margot Wallstrom, was in the country to visit some of the victims of the attack. She welcomed it as "a victory for justice".
"Let his apprehension be a signal to all perpetrators of sexual violence that impunity for these types of crimes is not accepted and that justice will prevail," she said.
A preliminary UN report into the attacks in July and August has found that at least 303 men, women and children were raped around Luvungi, in the Walikale region, some repeatedly, over a period of four days by around 200 armed rebels.
Another 214 unconfirmed cases of rape are under investigation in other areas of eastern DR Congo, according to the UN.
More than 1,000 homes and businesses were also looted and 166 people abducted for forced labour, says the report.
Victims interviewed said they believed the purpose of the attacks was to intimidate local people seen by the rebels as government supporters.
The UN mission in DR Congo (Monusco) has admitted it did not do enough to prevent the attacks, which took place only a few miles from a peacekeeping base.
A doctor from the International Medical Corps who visited rape victims in their villages, Dr Cris Baguma, said the rebels had come in peace and only began raping after being given food by the villagers.
"Men saw how they raped their wives, sons saw how they raped their mothers. Everyone in these villages is now very withdrawn and cold and in need of psychological assistance," he told Reuters news agency.
DR Congo's ambassador to the UK said he hoped the arrest would be a significant step to ending sexual violence in the east.
"If these soldiers and Mai Mai and all the militias that were following him know that their boss has been arrested and brought to justice, that will send a clear signal that their actions will not be tolerated," Kikaya bin Karubi told the BBC's Network Africa programme.
But Ms Wallstrom said the UN mission needed greater resources, and warned that if such attacks continued it would "brutalise the whole society, from generation to generation, and destroy all the values, all the standards".
DR Congo has a shocking reputation for sexual violence, and rape is commonly used as a weapon of war by a number of armed groups who continue to operate.
The UN says at least 8,300 rapes were reported in 2009 and it is believed that many more attacks go unreported.