In response, the United States Department of Defense, the UN peacekeeping department, and NATO last year each declared policies of "zero tolerance" for such abuses. They have initiated training for peacekeepers on issues like human trafficking and sexual abuse and have moved to tighten standards for forces serving under their command.
But as reports of abuses persist, international peacekeepers are facing calls for more stringent preventive measures.
A recent report from the Center for Strategic and International Studies (CSIS), a U.S.-based research institute, examined the Balkans, where thousands of women have been trafficked. The author of the report, Sarah Mendelson, tells RFE/RL her research found both a lack of awareness about trafficking and organizational cultures slow to change.
"What the report is about is a very large organizational dysfunctional response, inside the [U.S. Defense Department], inside NATO, inside the UN. They don't understand what they are looking at, and they're filled with all sorts of misperceptions about who these people are, how they came to be there, whether they want to be there or not, and it has led to a lot of inaction," Mendelson says.
Mendelson says the three organizations are at different stages of addressing the issue, but all have so far committed a low level of resources.
Concerning the U.S. military, her report alleges inadequate U.S. oversight of private military contractors. She cites what she calls a superficial investigation by military inspectors in 2003 into reports that employees for a Defense Department contractor exploited trafficked women while on assignment in Bosnia-Herzegovina.
Mendelson's critique of NATO focuses on the response of the alliance's leadership in Kosovo to evidence that troops from an affiliated Russian contingent were engaged in trafficking and running a brothel. In that episode, she charges that NATO officers in 2000 were instructed to ignore abuses against women and girls because the larger NATO-Russia relationship was too important to jeopardize.
At the United Nations, Mendelson says, senior officials have appeared more concerned with preserving troop contributions than responding vigorously to abuses committed by peacekeepers.
Mendelson stressed that the majority of peacekeepers perform their work honorably. But a failure to properly respond to problems like trafficking, she said, can cause great harm to missions.
"The reality is these organizations have for a long time either downplayed it or looked the other way. And you cannot talk about an effective peacekeeping mission if your peacekeepers are involved in undermining the rule of law. If you look the other way, if you purchase sex from a trafficker with a female who's been trafficked, you are helping to support organized crime," Mendelson says.
The issue has attracted the interest of the U.S. Congress. U.S. Representative Chris Smith plans to introduce a bill next month that would require safeguards to prevent peacekeepers from committing acts of sexual exploitation before a U.S. contribution to a UN peacekeeping mission is made.
Smith's bill also calls for further steps to ensure that U.S. government personnel and contractors are held to account.
But the three organizations cited in the CSIS report insist they have enacted meaningful measures to prevent sexual exploitation by peacekeepers.
A spokeswoman for the U.S. Defense Department, Lieutenant Colonel Ellen Krenke, wrote in an e-mail response to RFE/RL that the Pentagon has adopted a systemwide antitrafficking program that involves training for the department's military, civilian, and contract personnel serving abroad. The department is introducing a policy stipulating a clause on trafficking in employment contracts.
This month, Krenke said, the Defense Department has moved to implement a new measure that places civilian and civilian contract employees under the jurisdiction of the Pentagon.
NATO allies last year agreed that all personnel taking part in NATO-led operations should receive proper training in human trafficking.
NATO spokesman James Appathurai tells RFE/RL it remains the responsibility of national authorities to prosecute any soldier charged with abuses. But he stressed countries must commit to the NATO policy on trafficking abuses in order to participate in missions.
"We have set a very high bar here, and we intend, of course, to keep to it both for the military and the civilian side. This doesn't apply just to NATO forces but partner countries -- in other words, non-NATO countries that want to contribute to NATO-led peacekeeping operations have to sign up to the same standard," Appathurai says.
The trafficking problem is especially severe in the international protectorate of Kosovo, where it contributes to a thriving organized crime network. The concern about international workers rose again earlier this year when a staffer with the UN High Commissioner for Refugees was arrested on charges related to the sexual abuse of civilians in Kosovo.
The head of the UN mission in Kosovo, Soren Jessen-Petersen, says there are now a number of international and local nongovernmental organizations addressing the trafficking problem. But in a recent discussion with journalists, he acknowledged the challenges.
"Throughout the western Balkans, unfortunately, trafficking is happening all the time -- trafficking of women, all kind of criminal activities. And we have about 22,000 internationals, if you take the 17,000 of [the NATO-led peacekeeping force] KFOR and 6,000 in [the UN Mission in Kosovo] UNMIK, and I don't think they all came down there with angel wings on their back. We just have to make clear from the top that we convey clear messages, [that] we set clear examples of what is not tolerable," Jessen-Petersen said.
The United Nations has come in for especially intense scrutiny because of allegations that UN peacekeepers in Congo committed sexual crimes that included raping children.
In response, the organization has ordered peacekeeping troops not to associate with civilians in Congo. A UN spokesman announced on 17 March that the United Nations had fired one employee and suspended six over allegations of sexual misconduct in Congo.
But more far-reaching changes for UN peacekeeping are expected after the release of a report next week from a mission led by Jordan's UN ambassador, Zeid al-Hussein. He has been meeting with UN member states to come up with a plan to end incidents of sexual exploitation in UN missions.
The current practice has been to repatriate peacekeepers accused of misconduct. They face punishment from their home governments, but they are seldom prosecuted.