The head of UN Women has condemned the inadequate response to the widespread use of rape and sexual violence in conflicts, and warned that the amount of money dedicated to fighting such war crimes is shrinking.

Phumzile Mlambo-Ngcuka, executive director of the UN organisation dedicated to gender equality and empowerment, said “new types of violence and torture, worse than anything we’ve ever seen before” have been used against Rohingya women in Myanmar, yet only 2% of money sent to conflict settings is spent on improving women’s rights, while funding for UN Women fell 5% between 2013 and 2016.

Her warning follows criticism of the UK’s preventing sexual violence initiative, which since November 2012 has deployed 74 experts to 13 countries, but which campaigners say has been slow to respond to the Rohingya crisis. The initiative, set up in 2012 by Angelina Jolie and the then foreign secretary William Hague, established a team of experts who specialised in gathering evidence of sexual violence in conflict zones and who could respond promptly to crises.

Sources close to the Foreign Office say the initiative has also been hampered by a lack of leadership from the foreign secretary, Boris Johnson. “To make a difference, you have to have leadership from the very top,” said one source . “The policy shouldn’t be an irritant, it should be something we’re proud of … if we as a country stand for anything, these are the moments where we need to show what we’re made of.”

Andrew Mitchell, the former secretary for international development, said the initiative has the potential to bring perpetrators to justice, but that it needs to be used effectively. “The Foreign Office has seen some very good work collecting evidence of human rights abuses in the Syrian conflict, so its capacity to help and do work on this is real,” he said. “William Hague’s initiative needs to be used effectively to help and protect people who are going through hell.”

Campaigners say the initiative has helped raise the profile of sexual violence but, five years after its launch, it is unclear what impact it has had. “There have been a lot of questions around the amount of money that has gone into it versus what has come out of it and whether that money has been used in terms of on-the-ground services,” said Hillary Margolis, women’s rights researcher at Human Rights Watch (HRW). “Measuring outcomes and then reporting very transparently on that would be very welcome,” she added.

Mlambo-Ngcuka called on the international community to provide support and resources to Bangladesh, where more than 600,000 Rohingya have fled since a military crackdown on the minority group in Myanmar. “What I would encourage them to do is to make up and do their best because the need is still there and it’s [happening] now.” The level of brutality, and the vast numbers of people displaced, mean the situation is especially challenging, she said.

“The killing of babies and girls, throwing them in the water to poison the water so it’s not drinkable, the gang-raping of women and girls – it is very gruesome,” she said. “The situation, even if there is not violence, is complex, [because] there are a lot of unaccompanied children, and the girls among those children are destined to be exposed to violence. It has been going on for such a long time and it is not abating yet. We need sustained attention and we need to mobilise more resources in order to help the government in Bangladesh.” Providing safe accommodation to women was a priority, she said.

The Foreign Office said: “Education, changing attitudes and behaviours, is at the heart of preventing and responding to sexual violence in conflict ...

We continue to focus on tackling survivor stigma, securing justice and accountability, and preventing it from happening in the first place. We’ve trained over 17,000 military and police personnel around the world to prevent and respond to crimes of sexual violence.”