The cartoon shows a dog wearing an Israeli skullcap with the US written on its body. It is urinating on a statue of justice and eating a pile of bones.
The image is to make the point that the arrest warrant issued by the International Criminal Court for Col Muammar Gaddafi was politically motivated.
"I am deeply disturbed that once again UN Special Rapporteur Richard Falk has used his personal blog to publish abhorrent material," said Joseph M Torsella, US representative for UN Management and Reform.
"His shameful and outrageous behaviour is an embarrassment to the United Nations.
"Someone who vicious images has no place in the United Nations," Torsella said.
"We reiterate our call for him to step down."
An earlier post by Falk connected with 9/11 conspiracy theories had also upset the Americans.
He had written "what fuels suspicions of conspiracy is the reluctance to address the sort of awkward gaps and contradictions in the official explanations."
"Why not Syria in the current regional setting?" Falk had written under the cartoon, which he has now removed.
"And even more starkly, why not Gaza back in 2008-09 when it was being mercilessly attacked by Israel? The answers to such questions are blowin' in the wind."
In a post entitled - "my final attempt to clarify my posting of the cartoon", Falk says that he did not realise that the cartoon could be seen as anti-Semitic and pointed out that it would not have been on the Google search engine if it had.
"Even now I needed a magnifying glass to identify the anti-semitic character of the dog. My vision (at 80) is pretty good, but not good enough. It looked like a helmet to me, and the main visible symbol on the dog was the USA midriff covering," Falk writes.