Thousands of Haitians killed or sickened by a cholera epidemic that they blame on United Nations peacekeepers cannot sue the United Nations in a U.S. court because the UN has legal immunity that only it can waive, a judge has ruled.

In a decision late on Friday, Judge J. Paul Oetken of U.S. District Court in Manhattan dismissed a lawsuit filed by human rights lawyers seeking compensation for the cholera victims.

A lawyer for the plaintiffs said they would appeal the ruling.

The outbreak has killed more than 8,600 people and infected over 707,000 since October 2010, according to the UN.

Oetken wrote that the UN's ability to block lawsuits was established by a 1946 international convention and was made clear again in a 2010 ruling from a U.S. appeals court in a case of alleged sex discrimination.

"The UN is immune from suit unless it expressly waives its immunity," he wrote.

Appeal planned

The UN did not expressly waive immunity for the Haitians and has not accepted responsibility for the outbreak, although it has tried to raise money for a cholera elimination campaign.

The plaintiffs plan to appeal Oetken's ruling and show that their case is different from the 2010 case, said one of their lawyers, Brian Concannon, executive director of the Boston-based Institute for Justice & Democracy in Haiti.

"We are disappointed in the ruling but not discouraged, and we have always assumed that this case was going to go to the appeals court," Concannon said in a phone interview on Saturday.

Concannon said the UN was not entitled to immunity under the 1946 convention because it has failed to establish any kind of settlement process for the cholera victims, as required by the same convention.

Peacekeepers discharged raw sewage

UN spokeswoman Vannina Maestracci said the organization welcomed Friday's decision and was in the process of reviewing it further. "Our focus in Haiti remains on our commitment to eliminating cholera in Haiti," she said.

UN peacekeepers from Nepal likely caused the cholera outbreak when they were stationed near a major river and discharged raw sewage, according to the plaintiffs and a 2011 report from the U.S. Centers for Disease Control and Prevention.

Cholera, which had not been documented in Haiti in almost 100 years prior to the outbreak, is an infection that causes severe diarrhea that can lead to dehydration and death, and is caused by poor sanitation.