Prince Charles blamed an “influx of foreign Jews” to the Middle East as a cause of unrest in the region and called for the “Jewish lobby” to be challenged, it has been revealed.

The Prince of Wales made the comments in a letter to his close friend, the author Laurens van der Post in 1986.

The letter, published in the Mail on Sunday last weekend, was written as the prince was returning from a tour of Arab countries, during which he had “learnt a lot about the Middle East and Arab outlook” and had begun “to understand their point about Israel”.

The prince wrote: “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 the great problems.”

He appeared to suggest that Jewish influence in the United States had helped created conditions in which Arabs were driven to commit terrorist acts. He wrote: “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?”

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

A statement from Clarence House said 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 he has a “proven track record” of support for both Jewish and Arab communities.

Sources close to Prince Charles said friendships with Jewish figures, including the writer Simon Sebag Montefiore, meant he now held very different views on Israel and the Jewish community.