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Six Bangladeshi peacekeepers under United Nations command were demoted, dismissed or reprimanded for their roles in a sex-abuse case while on assignment in the Sudan, but U.N. officials are powerless to bring charges or prosecute the soldiers for their alleged crime.

Nonetheless, Jane Holl Lute, assistant secretary-general for peacekeeping operations, thinks the punishment is enough.

"I think it sent a very clear message," Lute told reporters Friday in response to growing questions about the U.N.'s handling of the case. News broke earlier this week that the peacekeepers were booted out of the Sudan within the past year after allegations surfaced.

The alleged incident involved one Bangladeshi soldier in June 2006, in Yambio in southern Sudan. An investigation by the U.N.'s Office of Internal Oversight Services is ongoing. One U.N. official told FOXNews.com the sexual exploitation allegations were "credible."

U.N. officials said four Bangladeshi peacekeepers were repatriated. But a handout from the U.N.'s Department of Peacekeeping Operations (DPKO) issued Friday, however, put that number at six.

One soldier was sent home and dismissed from the Bangladeshi army. The U.N. statement said two of the three guards on duty during the alleged incident who were sent home were lowered in rank and two superior officers were "severely reprimanded," according to a U.N. statement.

"The disposition of discipline" is up to troop contributing countries that are U.N. members, not the United Nations itself, Lute said.

In response to a question whether the U.N. requires a minimum code of justice for peacekeeping troops, Lute pointed to a proposal pending before the General Assembly that she said "strengthens measurably" the actions home countries take when their troops are accused of sexual abuse.

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If a member state isn't prepared to uphold those standards, she said, "then the organization is prepared to do without their services. We take this very seriously."

U.N. military officials have the power to direct the troops placed under their command, but are relatively powerless when it comes to punishing them if they are accused of crimes against humanity.

There are 13 misconduct investigations ongoing at the Sudan mission, some include sexual abuse.

From January 2004 to the end of November 2006, investigations were conducted for 319 sexual exploitation and abuse cases in U.N. missions throughout the world. These probes resulted in the dismissal of 18 civilians and the repatriation on disciplinary grounds of 17 police and 144 military personnel.

Lute: 'I'm Outraged'

"The reputation of U.N. peacekeeping is one of our most powerful assets, which is why we have responded over the past several years so strongly," Lute said. "The behavior of a relative few have tarnished the entire reputation of peacekeeping, and we will not allow that to occur."

Lute said any allegations of misconduct affect peacekeepers around the world, as well as the populations they work to protect.

"Every time I'm made aware of sex exploitation and abuse, I’m outraged. I'm outraged at every level — as a peacekeeper, as a professional, as a colleague of the tens of thousands of men and women who serve honorably in peacekeeping," said Lute, who served in the U.S. Army.

"I'm angry as a woman, I'm angry as a mother, I'm saddened that the world has not come as far as we'd like to believe in our treatment of women and vulnerable populations. I'm determined, I'm determined to do whatever it is we can to strengthen this comprehensive package of reform and remediation."

What's frustrating to military commanders on the ground is that there is little they can do to offending peacekeepers, other than putting them on desk duty, restricting them to quarters, and requesting a full investigation and repatriation.

"For peacekeeping, the United Nations depends on member states," U.N. spokeswoman Michele Montas told reporters Thursday. "They can only keep on asking to find out whether this is pursued farther.

"I think that's what they're trying to do. It's not a formal thing — it's a collaboration with those countries," she said, adding, "I don't know whether they [the U.N.] would be involved in the national jurisdictions."

She stressed the United Nations has a "zero impunity, zero tolerance" policy for such activity.

Montas said the United Nations is following up with Bangladeshi authorities to determine what's happened to the accused since they were sent back home a few months ago.

The Bangladesh Mission to the U.N. did not return phone calls by FOXNews.com for comment.

Because the United States is such a large contributor to peacekeeping missions, Anne Bayefsky, editor of Eye on the U.N., said, "the American taxpayer's entitled to ask some pretty hard questions about whether or not they should be funding, in effect, this egregious criminal behavior."

"The U.N. officially has a policy of 'zero tolerance' but the reality is that it's cognizant of these abuses for years," she added. "This is not an unfamiliar problem. The United Nations knows its peace operations are plagued with sexual exploitation and abuse and every once in a while, they produce another report saying 'we really have to ensure the zero tolerance policy is implemented,' yet the problem occurs over and over again so it's clearly not being implemented."

A spokesman at the U.S. Mission to the United Nations said "of course" the United States will make addressing peacekeeper abuse allegations a priority this year.

FOX News' Jonathan Wachtel contributed to this report.