The US on Wednesday rebuked a UN report that found the drone strike that killed a top Iranian general in Iraq was unlawful.
Qassem Suleimani, leader of Iran's Islamic Republic Guard Corps' Quds Force, and others died in the strike at Baghdad airport in January.
"It takes a special kind of intellectual dishonesty to issue a report condemning the US for acting in self-defence while whitewashing Gen Suleimani's notorious past as one of the world's deadliest terrorists," State Department spokeswoman Morgan Ortagus said.
"This tendentious and tedious report undermines human rights by giving a pass to terrorists, and it proves once again why America was right to leave" the UN Human Rights Council.
Agnes Callamard, the UN special rapporteur on extrajudicial, summary or arbitrary executions, found on Tuesday that Suleimani's killing breached the UN charter.
The report found the US failed to provide enough evidence of a continuing or imminent attack against its interests to justify the strike on his convoy, which also killed Abu Mahdi Al Muhandis, head of the Iran-backed Iraqi militia Kataib Hezbollah.
"Suleimani was in charge of Iran's military strategy and actions in Syria and Iraq," Ms Callamard wrote.
Ms Callamard called for accountability in killings by armed drones and for greater regulation of the weapons.
She will present her findings on Thursday to the Human Rights Council, from which US President Donald Trump withdrew in 2018, saying it was biased against Israel.
Mr Trump ordered the drone strike after escalating tension between the US and Iran, against which he has imposed sweeping unilateral sanctions.
Militia groups backed by Iran had been blamed for attacks on bases housing US troops and later for trashing the US embassy in Baghdad.
Trump administration officials later faced grilling by legislators, mainly Democrats, who said there was no evidence of an imminent attack that would legally justify killing Suleimani.
The Quds Force is the Guard's elite foreign operations branch.
A look back at the US attack on Suleimani
