Prince Charles attributed an “influx of foreign Jews” to the Middle East as a cause of unrest in the region in a letter to a friend, it has been revealed.

The letter, sent to author Laurens van der Post in 1986, also challenged the United States to “take on the Jewish lobby”.

The Prince of Wales added that the exodus of European Jews in the mid-20th century “helped to cause the great problems” in the Middle East since.

The letter, published in the Mail on Sunday today, read: “I now appreciate that Arabs and Jews were all a Semitic people originally + it is the influx of foreign, European Jews (especially from Poland, they say) which has helped to cause the great problems.

“I know there are so many complex issues, but how can there ever be an end to terrorism unless the causes are eliminated?

“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 letter was uncovered from a public archive, and was written following an official visit the then-38-year-old Prince made to Saudi Arabia, Bahrain and Qatar with Princess Diana.

He said he had “learned a lot about the Middle East and Arab outlook” from his visit.

A statement from Clarence House said that the opinions expressed in the letter were “not the Prince’s own views” but instead the reflected opinions of those he met on his trip.

It said: “The letter clearly states that these were not the Prince’s own views about Arab-Israeli issues but represented the opinions of some of those he met during his visit which he was keen to interrogate.

“He was sharing the arguments in private correspondence with a long standing friend in an attempt to improve his understanding of what he has always recognised is a deeply complex issue to which he was coming early on his own analysis in 1986.”

It added that the Prince of Wales has a “proven track record” of support for both Jewish and Arab communities.

Earlier this year it became known that an invitation for the Prince to Israel to mark the centenary of the Balfour Declaration was refused to avoid upsetting Arab nations.

Previously the heir to the throne caused controversy when, in 2014, he compared the actions of Russian president Vladimir Putin in Ukraine to those of Adolf Hitler.