Allegations of sexual abuse and exploitation by UN staff more than doubled last year, UN Secretary General Kofi Annan has said in a report.
The abuse allegations rocked the UN mission in DR Congo
Most of the allegations, which include rape, sexual assault and sex with minors, involved UN peacekeepers.
Mr Annan says he is "deeply troubled" by the increase.
On Friday, four Nepalese soldiers flew home to face sex abuse charges. They served with the UN in DR Congo, where claims of misconduct arose in 2003.
The Nepalese army said the men would be investigated, and court-martialled if the charges were found to have substance.
Allegations of misconduct by UN troops in DR Congo in 2003 sparked an inquiry and an overhaul of procedures.
"The increase in allegations is deeply troubling," Mr Annan says in the report.
"Although allegations have doubled since 2003, the Secretariat is aware that the data may still not reflect the true extent of these deplorable incidents."
A total of 121 allegations of sexual exploitation and abuse were registered last year.
The majority of these - 105 in total - were levelled against peacekeepers.
The report says more may come to light as people feel more confident that reporting incidents will result in action.
Almost half of the complaints against the peacekeeping troops involved sex with a minor and 15% involved rape or sexual assault.
Some 77,000 UN peacekeepers are deployed on missions including those in Ivory Coast, Liberia, DR Congo, Cambodia, Kosovo and East Timor.
Refugees and those fleeing conflict are often vulnerable to abuse
Ten claims were also made against UN civilian personnel working for the UN refugee agency, UNHCR.
The UN has recently published a series of guidelines to change the way peacekeeping operations are run.
The proposals include withholding pay for peacekeepers found guilty of sexual abuse, creating a fund to assist the victims, and establishing a uniform set of rules so that all peacekeepers - troops and civilians - are held to the same standards of conduct.
The report said that missions in Ivory Coast, Liberia, DR Congo, Ethiopia, Kosovo and East Timor have already established no-go areas for peacekeepers.
A non-fraternisation policy has also been introduced.
Some 53 uniformed peacekeepers were sent home last year after allegations made against them were substantiated, the report says.