"Donald Trump's ignorant view of Islam could make both of our countries less safe -- it risks alienating mainstream Muslims around the world and plays into the hands of the extremists," Khan said.
Khan is not the only foreign political figure to slam Trump's controversial policies. British Prime Minister David Cameron, French Prime Minister Manuel Valls and German Chancellor Angela Merkel have been among those to take issue with the positions the billionaire businessman has laid out during his run at the White House.
But there is also a pocket of European politicians that has embraced Trump -- primarily on the far right of the political spectrum in countries including Italy, Belgium and France. Many of these politicians blame immigrants for the lack of jobs and a stagnant economy, have called for tighter borders and endorsed bans on refugees due to the growing threat of radical Islamic terrorism.
That's no accident, said James Thurber, director of American University's European Public Affairs and Advocacy Institute.
"They're probably doing it because (Trump) is very similar to their policies in respect to immigrants, with respect to nativism and nationalism within their own nations," Thurber said.
Trump launched his presidential bid by proposing to build a wall along the U.S.-Mexican border to stem the flow of undocumented immigrants into the United States. Later in his campaign, the billionaire businessman called for a temporary ban on Muslim immigrants to the United States.
Like the Republican candidate, some European politicians have called for tightening the flow migrants and refugees from Africa and the Middle East in the wake of terrorist attacks in Paris and Brussels.
Thurber said struggling economies also have contributed to the fear of immigrants -- and the popularity of Trump and his right-wing European fans -- particularly in the polarized political environments in both Europe and the United States.
"They're worried about immigrants coming in and taking their jobs, they're worried about social expenditures for the immigrants when they've got tight budgets," he said. "I think a lot of people in the United States are worried about their jobs also and threats by immigrants."
Across the European continent, here's a look at the praise some politicians are offering Trump.
Trump gained a notable foreign boost from one of Italy's leading right-wing politicians, Matteo Salvini. The head of Italy's Northern League party met Trump at a rally in Philadelphia the day before the businessman's sweeping win in the Pennsylvania primary in April.
The conservative Italian politician tweeted a picture of himself and the GOP front-runner and -- in Italian -- offered praise for the former reality TV star as well as criticism for President Barack Obama.
The Trump campaign did not return a request for comment on Salvini's endorsement.
Salvini is known to be a vocal supporter of Italian fascist leader Benito Mussolini. In February, Salvini praised the Italian dictator for doing "so many good things."
Trump has also indirectly referenced Mussolini in a positive light. The real estate mogul retweeted a quote attributed to the dictator in February.
Asked about associating himself with the Italian dictator, Trump told NBC's Chuck Todd on "Meet the Press": "Look, Mussolini was Mussolini ... I know who said it. But what difference does it make whether it's Mussolini or somebody else? It's certainly a very interesting quote."
The former leader of France's National Front Party, Jean-Marie Le Pen, backed Trump earlier this year, tweeting: "If I were American, I'd vote Donald Trump ... but God bless him!"
Le Pen's daughter and current party leader, Marine Le Pen, has not endorsed Trump, though, and has said his proposed ban on Muslims is a step too far.
While the British Parliament debated banning Trump from the United Kingdom, the real estate tycoon found some support among the leader of the United Kingdom's Independence Party.
"I think that a man that has run a business, and made a fortune, maybe we are underestimating his ability," Nigel Farage, head of UKIP, was quoted telling the U.K.'s Daily Express
However, like Marine Le Pen, Farage has spoken out against Trump's proposed ban on Muslim immigrants to the United States, calling it a "political mistake, too far.
Trump gained the support of Geert Wilders, leader of the anti-immigration Dutch Freedom Party, in December. Wilders tweeted he hoped the GOP front-runner would be the next U.S. president.
Like Trump, Wilders called for stricter immigration policies in the wake of the Paris attacks last November. The Dutch politician advocated for immediately sealing the Dutch border.
Trump harshly criticized Belgium's handling of terrorism
in the aftermath of the Paris and Brussels attacks, calling the European capitol a "disaster city."
However, the GOP front-runner was able to garner support from Belgium's right-wing People's Party, led by Mischaël Modrikamen.
In a video released on the day of the Brussels terror attacks, Modrikamen said he "fully supports Donald Trump."
"America should not become another Brussels," Modrikamen said, mirroring Trump's comments. "Brussels is becoming another third-world city, with a majority of Muslim immigrants."
While Trump enjoys the support of some far-right politicians, most of the international reviews of the Republican candidate have been negative.
Secretary of State John Kerry said he is frequently asked
about Trump's candidacy during foreign trips.
"Every meeting I have, everywhere, people are asking, 'What is happening with the United States? What are you doing to yourselves?' " Kerry said in a recent interview.
A number of world leaders
spoke out against Trump after he proposed a ban on Muslim foreigners.
France's Prime Minister Manuel Valls said Trump "feeds the hatred and confusion."
Britain's Cameron called the comments "divisive, unhelpful and quite simply wrong."
Since Trump became the presumptive Republican nominee, Cameron has changed his tone
, saying Trump "deserves our respect" for making it through the primaries.
However, the conservative leader said his views about Trump's proposed ban on Muslims remain the same.
"I'm very clear that the policy idea that was put forward was wrong, is wrong, and will remain wrong, so I'm very clear on that," Cameron said.