He wrote to Catholic and Anglican leaders to say that reports of serious attacks on migrants "have caused deep concerns to the Polish nation in general, and to myself in person."

Such attacks included the murder of Arkadiusz Jozwik, 40, who was beaten to death by a teenage mob in Harlow, England, Aug. 27, he said.

Duda urged Cardinal Vincent Nichols of Westminster, president of the Bishops' Conference of England and Wales, and Archbishop Justin Welby, leader of the Worldwide Anglican Communion, to do whatever they could at the parish level to prevent such violence against Poles.

In his Sept. 5 letters, the president pleaded for a "constructive effort" for local parishes "to alleviate the adverse consequences of intolerance and xenophobia, including what appears to be a clear instance of aversion and animosity toward Poles."

"I am sure Your Eminence will agree that it is of utmost importance that these incidents do not occur again, as they have a potential of creating a formidable ridge between the Polish and English people," he said in his letter to Cardinal Nichols. "This could, in turn, lead to the erosion of the local community, characterized by a genuinely positive presence of Poles in England," he said, adding that Poles had strived to make a huge contribution to the socio-economic condition of the U.K.

"Only through mutual understanding and consideration for one another can a thriving community be achieved," he added.

Since Poland joined the European Union in 2004 some 800,000 Poles have migrated to the U.K., making them the largest ethnic minority in the country. After the U.K. voted to leave the European Union in a June 23 referendum, fought largely over the issue of mass migration, they became targets of xenophobic violence and abuse.

Police revealed that 3,000 so-called "hate crimes" and incidents were also reported between June 16 and June 30, a 42 percent increase over the same period in 2015. The peak day for offenses was June 25, when 289 crimes of a xenophobic or racist nature allegedly were committed. These included an arson attack on a Polish property in Plymouth and the vandalism of buildings of a Polish social and cultural association in west London.

In Wigan and Cambridge, laminated cards reading "No Polish vermin" in both England and Polish were pushed through the letter boxes of the homes of some European migrants.

A man was arrested for painting a swastika into the door of a business in Shrewsbury and, at a rally in Newcastle, nationalists unfurled a banner that demanded: "Stop Immigration, Start Repatriation."

Archbishop Welby later told the House of Lords that the upsurge in xenophobia represented an outpouring "of poison and hatred" in a manner he had not seen "in this country for very many years."

Cardinal Nichols also denounced the violence, saying in a June statement that "this upsurge of racism, of hatred toward others, is something we must not tolerate."

"We have to say this is simply not acceptable in a humane society, and it should never be provoked or promoted," he said.

"We need to grasp again our basic sense of purpose; in living together, creating together and fashioning a society," the cardinal added.

Jakub Krupa, a trustee of London's Polish Social and Cultural Association, which was vandalized after the referendum, said he believed the vast majority of people who voted to leave the EU had "perfectly noble and good reasons."

He said he thought that a small minority of people with xenophobic or racist views had been emboldened by the result because they wrongly concluded that the public shared their opinions.

"It is about all migrants," Krupa told Catholic News Service in a Sept. 8 interview, "but Poles are the most visible group and, therefore, the most vulnerable."

"The majority of British people are fantastically welcoming people who have been supporting the Polish community over the years," he added. "This is something we have to focus on but, nevertheless, we have to keep in mind the negative incidents so that we can be sure the police and politicians are aware of the problems so they can fix them."