The Muslim Brotherhood is a puppet political formation created by Jews to destabilise Egypt and neighbouring Muslim countries, according to a conspiracy theory denounced by the Anti-Defamation League.
ADL discovered the theory circulating among opponents of the Egyptian president Mohammed Mursi and adversaries of the pan-Arab Islamic movement around the world.
"However bizarre and ludicrous, it is an increasingly popular conspiracy theory that the Muslim Brotherhood is a Jewish production to destroy Egyptians," said ADL firector Abraham Foxman.
"It would seem that no allegation made against the Jews and Israel is too absurd when it is used to stigmatise and discredit others in the Arab world."
Amid escalating unrest against Mursi's rule in Egypt, a group of protesters in the northern city of Port Said were caught on camera chanting "The Brothers [Muslim Brotherhood] are Jews."
The theory was backed by Dubai police chief Lt Gen Dahi Khalfan, who conveyed numerous messages to his his 365,000 Twitter followers that the Brotherhood was a Jewish conspiracy.
Khalfan, a member of the executive council of the government of Dubai, also retweeted a link to a YouTube video entitled: "The Jewish-Muslim Brotherhood alliance and the project of establishing Greater Israel".
"The Muslim Brotherhood has a long history of articulating its historical and ideological opposition to the existence of the state of Israel and Brotherhood leaders, including President Mohammed Mursi, have a long history of making anti-Israel and anti-Semitic statements," ADL said.
Meanwhile, Mursi has welcomed Iranian president Mahmoud Ahmadinejad, a vociferous opponent of Israel, to Egypt. Ahmadinejad, who said he wanted to see Israel wiped off the world map, once described the Jewish state as a cancerous tumour.
He is the first Iranian leader to be received in Cairo in more than 30 years.