The United Nations ducked behind a screen of diplomatic immunity on Thursday and rejected a claim for damages on behalf of more than 5,000 Haitian cholera victims and their families.
The claim had been filed in November 2011 by the Institute for Justice and Democracy in Haiti (IJDH), a Boston-based human rights group.
It said the UN and its peacekeeping force were liable for hundreds of millions of pounds for not properly screening its soldiers.
The IJDH cited studies showing that cholera had been brought to Haiti by troops from Nepal, where it is endemic.
A local contractor failed to properly sanitise the waste of a UN base and the bacteria leaked into a tributary of one of Haiti's biggest rivers, according to a study by a UN-appointed panel.
Cholera has sickened nearly 500,000 people and killed over 7,750 since the outbreak began in October 2010, according to the Haitian government.
Secretary-general Ban Ki-moon called Haitian President Michel Martelly to inform him of the decision "and to reiterate the commitment of the UN to the elimination of cholera in Haiti," a spokesman said.
IJDH director Brian Concannon retorted that, after 15 months, the rejection had been a single sentence which said the claims are "not receivable" because they concern "a review of political and policy matters."
He said: "Our case is about the UN dumping contaminated sewage in Haiti's waters that has caused thousands of deaths.
"Under this definition, any harm that the UN does to anybody would be a matter of policy."
Mr Concannon said: "We're disappointed because the UN is passing up a chance to stop cholera's killing and to show leadership in promoting the rule of law."
Lead counsel for the victims Mario Joseph added: "It is disgraceful that the UN will not even consider compensating the thousands of families who have lost their children, mothers, fathers, brothers and sisters due to UN wrongdoing."
Mr Concannon, a co-counsel for the victims, said that the institute's next step will be to go to a national court to seek compensation for the victims.
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