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LONDON — Reports of racial abuse on Britain's streets have spiked following the country's bitterly fought Brexit referendum, campaigners say.

More than 100 alleged hate crimes have been brought to the attention of the Muslim Council of Britain since Friday's result.

Immigration was among the chief concerns of "Leave" voters, according to pollsters, and the "Remain" campaign accused some of its opponents of encouraging racist and xenophobic attitudes.

In the wake of the "Leave" victory — 17.4 million votes to 16.1 million — dozens of people posted on social media that they had suffered or witnessed racial abuse by people apparently using the result to legitimize their views.

This evening my daughter left work in Birmingham and saw group of lads corner a Muslim girl shouting "Get out, we voted leave". Awful times — Heaven Crawley (@heavencrawley) June 24, 2016

"Table next to me says to Polish waitress "How come you're so cheerful? You're going home." Him and the missus started laughing." Disgusting — Jamie Pohotsky (@jamiepohotsky) June 24, 2016

Just arrived at a 78% Muslim school. White man stood making victory signs at families walking past. This is the racism we have legitimised. — Dr Karen Bateson (@KarenJBateson) June 24, 2016

My home town of Newcastle. This afternoon. I feel like I am back in the 1980s. pic.twitter.com/8THD1xsn1N — David Olusoga (@DavidOlusoga) June 25, 2016

Gloucester @Tesco: 'this is England, foreigners have 48 hours to f**k right off. Who is foreign here? Anyone foreign?' #Brexit — Max Fras (@fullofeels) June 24, 2016

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Man in Kings X station yells ‘BREXIT’ in my south Asian friend’s face. Within 10 hours of the result I experienced 2 racialised altercations — kerem (@KeremBrulee) June 25, 2016

Been standing here five minutes. Three different people have shouted "send them home". pic.twitter.com/cVvmYvC73o — Ciaran Jenkins (@C4Ciaran) June 24, 2016

Armed Forces Day Parade, Romford. Until the last photo, the scariest thing was the Brownies bringing up the rear. pic.twitter.com/GX5JmBT7L9 — diamond geezer (@diamondgeezer) June 25, 2016

Shuja Shafi, the Muslim Council of Britain's secretary, said in a statement that Britain was "witnessing the shocking extent" of the divisions that emerged during the campaign, "with reports around the country of hate speech and minorities being targeted."

Following these reports, London Mayor Sadiq Khan said in a statement Monday he had "asked police to be extra vigilant for any rise in case of hate crime," the Evening Standard reported. Almost 60 percent of Londoners voted "Remain" but Khan said it was important not to "demonize" the 1.5 million people in the capital who voted "Leave."

A Facebook group called "Worrying Signs" was set up to document these reported incidents and by Monday morning gained more than 5,000 members in 12 hours.

"People have been reporting some really harrowing experiences," said group co-founder Natasha Blank, a 32-year-old marketing professional and freelance writer from the English city of Manchester.

Blank was keen to stress that these views were not representative of the vast number of "Leave" voters, some of whom were members of the Facebook group and also condemned the alleged incidents.

Union flags hang between buildings along London's Oxford Street on Monday. ODD ANDERSEN / AFP - Getty Images

She has not had time to analyze how many individual incidents have been posted, nor verify their veracity. But for Blank, whose family heritage is Pakistani, the mood has been undeniable.

"It's so bizarre and difficult to explain but you can almost feel it," she said. "I went with my mother to vote and the air was thick with something insidious."

What had already been a tense campaign boiled over on June 16 just one week before the vote.

Nigel Farage, leader of the right-wing United Kingdom Independence Party, or UKIP, unveiled a poster featuring a line of migrants and refugees crossing the Croatia-Slovenia border in 2015.

Over the image was the text "BREAKING POINT." Some commentators on social media pointed out the image's inadvertent similarities to Nazi propaganda from the 1930s.

Your new poster resembles outright Nazi propaganda, @Nigel_Farage. Thanks to @brendanjharkin for pointing it out. pic.twitter.com/Rd89XZSvfD — Connor Beaton (@zcbeaton) June 16, 2016

Just hours later, pro-EU lawmaker Jo Cox was allegedly murdered by a man who later gave his name in court as "death to traitors, freedom for Britain."

Boris Johnson, former London mayor and leading voice in the Leave campaign, appeared to play down any divisions that had built up during the referendum campaign.

Pro-Brexit campaigner Boris Johnson leaves his London home on Monday. Getty Images

Writing in the Daily Telegraph newspaper, he said sovereignty — relating to the Euroskeptic idea that the EU makes too many of Britain's laws — was the main reason people voted to leave the EU, rather than immigration.

(Most pollsters agree that sovereignty was the main reason people said they voted "Leave," with immigration and border control coming second.)

Johnson said the "negative consequences are being wildly overdone," also referencing the political and economic uncertainly currently shrouding the U.K.

Among the reported incidents of alleged racist abuse, staff at London's Polish Social and Cultural Association came into work Sunday morning to find "really unpleasant graffiti all across the front of our building," association chair Joanna Mludzinska said.

We are gratelul for the local support says POSK's Chair Joanna Mludzinska following today's incident. pic.twitter.com/gtURQUubn6 — POSK London (@posklondon) June 26, 2016

London's Metropolitan Police said it was investigating the graffiti as "alleged racially motivated criminal damage" but added there had been no arrests.

A spokeswoman for the force told NBC News that officers were looking into media requests for the number of racial abuse reports since Friday. Jess Phillips, a lawmaker for the opposition Labour party, said she would be formally asking the government for the figures.

I will be putting in a parliamentary question to find out all incidents of racial hatred in the UK this weekend compared with last week — Jess Phillips MP (@jessphillips) June 25, 2016

In Cambridge, laminated signs reading "leave the EU, no more Polish vermin" were found outside schools hours after the result was announced Friday, the Cambridge News reported.

A Polish student who found some of the signs told the newspaper that he "felt really sad" at the message, and police were investigating, according to the report.