Prince Charles is facing a backlash over a letter he wrote in 1986 in which he urged the US to "take on the Jewish lobby" and blamed "the influx of foreign Jews" for the unrest in the Middle East.

The chairman of the Campaign Against Antisemitism has called the letter "disturbing" and the comments as "unmistakably anti-Semitic".

The letter, which was released by The Mail on Sunday, was written to the prince's close friend Laurens van der Post and discusses the unrest in the Middle East and the creation of Israel.

"I now appreciate that Arabs and Jews were all a Semitic people originally and it is the influx of foreign, European Jews (especially from Poland they say) which has helped to cause great problems," Charles wrote. The prince referred to this influx of European Jews as the cause of terrorism in the region.

He continued: "Surely some US president has to have the courage to stand up and take on the Jewish lobby in the US? I must be naïve, I suppose!"

The term "Jewish lobby" is considered to be anti-Semitic because it suggests that wealthy Jews in the US exercise disproportionate influence over government policy, MailOnline reported.

"This letter is disturbing. It appears that our future king believed in 1986 that the 'influx' of Holocaust survivors to Israel were not 'Semitic', 'cause great problems' including terrorism, and should be 'eliminated', presumably through their removal," Gideon Falter, chairman of Campaign Against Antisemitism, said in a statement.

Falter added that since the letter was written, it appears Prince Charles has "warmed" to the Jewish community. He said that in order to "reassure the worldwide Jewish community" that he has changed his views, "these historic remarks must urgently be repudiated by Prince Charles".

Stephen Pollard, editor of The Jewish Chronicle, also criticised the letter, calling it "jaw-droppingly shocking". "That they [the Prince's comments] come from the heir to the throne is unsettling, to put it mildly."

The MailOnline noted that the Prince of Wales has many prominent Jewish friends and in 2013 became the first Royal to attend a chief rabbi's inauguration ceremony. Charles also expressed concerned in a 2013 speech on the apparent rise of anti-Semitism in Britain.