Republican presidential front-runner Donald Trump slammed a U.K. petition which seeks to bar him from visiting the European nation in the wake of his controversial proposal that foreign Muslims be prohibited from entering the U.S. temporarily.

“The United Kingdom is trying hard to disguise their massive Muslim problem. Everybody is wise to what is happening, very sad! Be honest,” Trump tweeted Thursday. The real estate mogul also praised controversial British columnist and former “Apprentice” contestant Katie Hopkins for her “powerful writing on the U.K.’s Muslim problems.”

The online petition currently has over 400,000 signatories which means, based on British parliamentary rules, it will be debated by top officials in the government. “The UK has banned entry to many individuals for hate speech. The same principles should apply to everyone who wishes to enter the UK,” the petition reads. “If the United Kingdom is to continue applying the ‘unacceptable behaviour’ criteria to those who wish to enter its borders, it must be fairly applied to the rich as well as poor, and the weak as well as powerful.”

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Meanwhile, London’s mayor Boris Johnson has said Donald Trump is “clearly out of his mind,” and British Prime MInister David Cameron has condemned Trump’s position on Muslim entry into the U.S. as “divisive, unhelpful and quite simply wrong.”

Trump is also getting criticized by his own Republican peers, with most of his 2016 competition coming forward to attack his stance on Muslims. Still, a recent Bloomberg Politics/Purple Strategies poll has found that two thirds of the GOP primary electorate back Trump’s polarizing proposal and he remains solidly in first place in most polls of the Republican race for the presidential nomination. He has insisted that he will “never” drop out of race.

“I have an awfully good chance of becoming the nominee,” Trump said during a CNN interview on Wednesday.

As for Hopkins, she has defended Trump in the past over allegations of religious and racial prejudice, but she herself has been the subject of considerable backlash for her comments on migrants and Muslims. She compared migrants to ”cockroaches” and “feral humans” (which drew a rebuke from the United Nations) and was investigated for “inciting racial hatred” earlier this year. She once tweeted “I get grumpy when I don’t eat – but I don’t blow things up,” while describing a spike in Middle East violence over the Ramadan holiday. Last year, a series of anti-Muslim tweets appeared on Hopkins’ Twitter account, including one that referred to Palestinians as “filthy rodents,” which led to calls for her arrest.