Britain's Prince Charles said the numbers of vulnerable young Muslims being radicalized by "crazy stuff" on the Internet was "frightening", in an interview to be broadcast Sunday and of which excerpts were released Saturday night.
The heir to the throne also voiced concern about Christians fleeing the Middle East in droves, saying the situation might end with very few left in the cradle of the religion.
In the BBC radio interview, excerpts of which were quoted by AFP, Prince Charles said radicalization was "one of the greatest worries" and the issue could not be simply "swept under the carpet.
"It's the extent which this is happening is the alarming part," the 66-year-old said.
Speaking of "the values we hold dear", Charles added, "You'd think that the people who have come here, born here, go to school here would abide by those values and outlooks.
"But, the frightening part is that people can be so radicalized either through contact with somebody else or through the Internet and the extraordinary amount of crazy stuff which is on the Internet," he added.
"Some aspect of this radicalization is a search for adventure and excitement at a particular age," he said.
The Prince of Wales said much of his own work with young people in deprived areas had been aimed at finding "constructive paths" for people to channel their energies.
"There are some really interesting examples of how people can be de-radicalized once they become radicalized because I think sometimes they find they are horrified by what it leads to," he told BBC radio.
He said more people now realized they had to address prevention, adding, "You can't just sweep it under the carpet."
Charles said the numbers of Christians in the Middle East was going "dramatically down", with people "intimidated to a degree you can't believe" where the Islamic State (ISIS) jihadist group has taken control in northern Iraq.
"There is a danger that there is going to be very, very few left," he warned.
"Christians have been in the Middle East for 2,000 years. Before Islam came in the 8th century. And have contributed an enormous amount, as many Muslims and others would agree.
"So that makes it an even greater tragedy," said Prince Charles, who is visiting Jordan, Kuwait, Saudi Arabia, Qatar and the United Arab Emirates from Saturday to Thursday.
The remarks come as thousands of European Muslims have reportedly flocked to join ISIS in Iraq and Syria. These include at least several hundred from the UK, although some estimates put that figure at 1,000, and officials have admitted the precise figure is not yet known.
In November, two brothers became the first Britons to be jailed for terrorism training in Syria, after they had admitted conspiracy to attend a terrorism training camp in 2013.
A month later, a British mother of six who hoped one of her sons would become a jihadist was jailed for five years and three months after she used social media to encourage acts of terror in Syria.
The danger from radicalized Britons was illustrated in October, when a four-man ISIS terror cell was busted by police before apparently planning to behead one or several Britons on the streets of London.