UN agencies in charge of refugee camps for victims of Haiti's earthquake are inexperienced and dysfunctional, the US charity Refugees International says.
The groups say reports of gang rapes are common, and a lack of translators means UN police cannot do their job.
A UN spokeswoman told the BBC that the organisation was doing its best, but said the scale of the disaster made their job very difficult.
More than a million people were left homeless by the quake.
Former US President Bill Clinton, who has been visiting a camp, has vowed that US aid long promised to Haiti but yet to materialise will soon be released.
Refugees International, in its report titled Haiti: Still Trapped in the Emergency Phase, said the people of Haiti were "still living in a state of emergency, with a humanitarian response that appears paralysed".
"Living in squalid, overcrowded camps for a prolonged period has led to aggravated levels of violence and appalling standards of living," the report says.
"Despite these alarming conditions, the UN co-ordination system in Haiti is not prioritising activities to protect people's rights."
The group's spokeswoman Melanie Teff, who took part in a recent fact-finding trip to Haiti, told the BBC that many of the camps had no police presence.
"I spoke with women's groups, who told me of women being forced to exchange sex for food because they were so desperate, in order to support their families," Ms Teff said.
She said reports of gang rape were common, and in some camps, the security committees were run by members of the local gang.
But the UN's Imogen Wall defended the organisation, saying the camps were relatively peaceful places, and that the UN had doubled the numbers of police since September.
"We've had very, very few security incidents in the camps," she said.
"People do expect the UN to solve everything, but we have deep and endemic problems here that need very long-term and committed solutions."
She said many of the problems Haiti faced - including high rates of sexual violence - had plagued the Caribbean nation before the quake, and had little connection to the refugee camps.
But she said the priority for the UN was to get the people out of the camps.
Meanwhile, Mr Clinton, who co-chairs the UN commission overseeing Haiti's reconstruction, heard the concerns of Haitians on Wednesday as he toured a large camp in the capital, Port-au-Prince.
Mr Clinton's foundation pledged $500,000 (£313,000) to help the camp, which is located on a former golf course.
The former US president spoke of his frustration about the slow arrival of funding - with the US still to deliver on any of the $1.15bn of aid promised at a donors' conference in March.
"In the next day or so, it will become obvious that the United States is making a huge downpayment on that," Mr Clinton said, without elaborating.
The former president said that the money was being held up by a "rather bizarre system of rules" in the US Senate.