Hollywood star Angelina Jolie and British Foreign Secretary William Hague on Tuesday launched a four-day summit on ending rape in war, calling for an end to the "culture of impunity" and more prosecutions.
US Secretary of State John Kerry, who will attend the conference in London on Friday, said the delegates from 117 countries wanted to "relegate sexual violence to the annals of history".
The summit is the fruit of a two-year campaign by UN special envoy Jolie and Hague, who have visited the Democratic Republic of Congo and Bosnia to meet victims of rape during conflict.
As she opened the conference, Jolie said she and Hague had discussed a woman they met in Bosnia, who was still too ashamed to tell her son that she had been raped.
"This day is for her," said Jolie. "We believe it truly is a summit like no other."
Standing next to her, Hague told reporters: "This will be the greatest concentration of effort, of discussion and decision ever seen in combating sexual violence in conflict."
The conference, held at a vast conference centre, includes 150 events open to the public in what the organisers hope will be a giant exercise in raising awareness.
In a statement, Kerry called for countries to end their protection of individuals who commit "these vile acts".
"We must declare in unison: 'They can't run and they won't hide here'," he said.
Almost 150 governments have endorsed a declaration of commitment to end sexual violence in conflict.
Organisers also want to increase and improve the documentation of rape in warzones to allow more prosecutions to be brought.
Liesl Gerntholtz, of Human Rights Watch, told AFP that while most victims were women and girls, "there's an emerging body of research and documentation that certainly shows that men have been targeted".
She said: "Human Rights Watch's own research shows that in Syria and Libya sexual violence against men has been part of the pattern of sexualised torture, particularly for men who are in detention or who are being held by the regime or militia."
Hague has said it was Jolie's film "In the Land of Blood and Honey" that alerted him to the extent of sexual violence in conflict zones.
The 2011 film, which marked Jolie's directorial debut, is a love story told against the backdrop of the Bosnian war two decades ago, when according to Hague some 50,000 women were raped.
Jineth Bedoya Lima, a journalist who endured sexual violence in Colombia's conflict, will speak at the conference.
"For the first time in history a world summit highlights and denounces a crime that is normally made invisible and is often silenced by the majority of states," she said.
Hague and Jolie will take part in meetings with youth delegates on Tuesday and on Wednesday are due to launch an international protocol.
On the sidelines of the summit on Thursday, Hague will chair a ministerial meeting on security in northern Nigeria in the wake of the kidnap of hundreds of schoolgirls by the Al-Qaeda-linked Boko Haram movement.
UN Secretary General Ban Ki Moon -- by video message -- and US Secretary of State John Kerry will speak in a closing plenary session on Friday.