By Anastasia Moloney

BOGOTA (Thomson Reuters Foundation) - A U.S. federal appeals court has upheld the United Nations' immunity from a damage claim filed by human rights lawyers on behalf of thousands of Haitians killed or sickened by a cholera epidemic they blame on U.N. peacekeepers.

In a decision late on Thursday, the U.S. Second Circuit Court of Appeals in New York upheld a lower court's January 2015 dismissal of a lawsuit brought by lawyers seeking compensation and a public apology for 5,000 Haitian cholera victims.

"We have considered all of plaintiffs' arguments on appeal and find them to be without merit," the U.S. appellate judges concluded.

Cholera, a water-borne disease, has killed more than 9,000 Haitians and infected over 770,000 since the outbreak began in 2010, U.N. figures show.

The court's decision came shortly after Farhan Haq, spokesman for U.N. Secretary-General Ban Ki-moon, admitted the U.N.'s possible involvement in the introduction of cholera to Haiti.

"...over the past year the U.N. has become convinced it needs to do much more regarding its own involvement in the initial outbreak and the suffering of those affected by cholera," he told reporters on Thursday.

Lawyers for the plaintiffs said the remarks were a breakthrough because it was the first time the U.N. had acknowledged any involvement in causing the cholera outbreak.

A 2011 study by the U.S. Centers for Disease Control and Prevention said U.N. peacekeepers from Nepal, where cholera is endemic, were the likely cause of the outbreak. The peacekeepers on mission in Haiti were stationed near a river and discharged raw sewage.

Brian Concannon, executive director of the Boston-based Institute for Justice and Democracy in Haiti (IJDH), the group that filed the lawsuit on behalf of cholera victims, said they had 90 days to decide whether to seek an appeal with the U.S. Supreme Court.

"We will decide how to proceed based on whether the U.N.'s actions fulfill the cholera victims' rights to an effective remedy," Concannon said in a statement.

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A previous January 2015 ruling on the cholera case by a U.S. court said that the U.N. can block lawsuits established by a 1946 international convention and is thus immune to such legal action.

But lawyers for the plaintiffs have long argued that the U.N. is not entitled to immunity under the convention because it has failed to establish any kind of settlement process for the cholera victims, as required by the same convention.

"This outcome places the onus back on the U.N. to follow through on its commitments to respond justly to victims out of court if it does not want to be an organization that stands for impunity," Mario Joseph, a Haitian lawyer who heads the Bureau des Avocats Internationaux, IJDH's partner in Haiti, said in a statement.

Health experts say cholera, which had not been documented in Haiti in almost 100 years prior to the outbreak, will continue to kill and infect Haitians as long as they lack access to clean water and sanitation.

(Reporting by Anastasia Moloney, editing by Ros Russell.; Please credit the Thomson Reuters Foundation, the charitable arm of Thomson Reuters, that covers humanitarian news, women's rights, trafficking, corruption and climate change. Visit http://news.trust.org)