The U.N.peacekeepingmission in Haiti, one of the world's longest-running such deployments and the only one in the Americas, will end in a few months, but not before reckoning with a fresh scandal.

A U.N.battalionof Nepalese peacekeepers in 2010 introduced a lethal strain of cholera to Haiti, where it has since killed more than 9,000 people and infected hundreds of thousands. Now, the Associated Press reports that at least 134 U.N.peacekeepersfrom Sri Lanka took part in a sex ring in Haiti that victimized nine children, the youngest just 12, from 2004 to 2007. The report should serve notice that U.N.peacekeepingoperations worldwidearebadly in need of reform and oversight.

The sex ring was part of what appears to have been a broader pattern of sexual exploitation and abuse, along with impunity, that has marked the U.N.missionin Haiti since it began in 2004 after an elected president was overthrown. The A.P.turnedup hundreds of allegations of abuse in Haiti, many of themcoldbloodedand horrific, carried out by peacekeepers from Bangladesh, Brazil, Jordan, Nigeria, Pakistan, Uruguay and Sri Lanka. In very few cases did the troops face discipline.

The U.N.announcementlastweek that the mission in Haiti would be wound down over the coming six months was unrelated to the A.P.'s nearly simultaneous revelations of sex abuse by peacekeepers. Thetroops'withdrawal - they'll be replaced by a much smaller contingent of police trainers - reflects both the country's progress toward stabilization after successful elections and financial pressure to trim peacekeeping operations, owing partly to the Trump administration's threat to cut U.S.contributionsto the multinational organizationbyhundreds of millions of dollars.

Even when the mission in Haiti is wrapped up, the United Nations will have more than a dozen peacekeeping missions worldwide; Haiti is by no means the only place peacekeepers have treated as a sexual playground. The United Nations must insist, as a precondition for accepting peacekeeping troops, that contributing countries will court-martial and punish soldiers who commit abuse. It should also sever payments to peacekeeping contingents implicated in sexual abuse if they fail to impose discipline. In the absence of such accountability, peacekeeping missions may do more harm than good.

Haiti may have been especially vulnerable to exploitation by peacekeepers as the hemisphere's poorest nation, leveled by a devastating earthquake in 2010 and a hurricane last year. Some children and teens reportedly were raped outright; others engaged in what victims called "survival sex," coerced into trading their bodies for scraps of food or a few dollars.

The United Nationsinsistsit is making progress in holding peacekeeper-contributing countries to account; it said much the same thing a decade ago.