The United States said UN expert Richard Falk was "biased" in calling for an investigation on Israel's January offensive in the Gaza Strip on grounds it could be construed as a war crime.
"Look, we've expressed our concern many times about the special rapporteur's views on dealing with that question," State Department spokesman Robert Wood told a press briefing on Monday.
"We've found the rapporteur's views to be anything but fair. We find them to be biased. We've made that very clear," he added.
In a report presented on Monday at the Geneva-based UN Human Rights Council, UN expert on the Palestinian territories Falk called for a probe to assess if the Israeli forces could differentiate between civilian and military targets in Gaza.
"If it is not possible to do so, then launching the attacks is inherently unlawful, and would seem to constitute a war crime of the greatest magnitude under international law," Falk said in the report.
"On the basis of the preliminary evidence available, there is reason to reach this conclusion," he added, pointing out that attacks were targeted at densely populated areas.
Wood said the United States was aware it could not prevent an investigation, but stressed: "if there are going to be these types of investigations, they need to be non-biased.