The Muslim mayor of London has issued a warning to Donald Trump: Moderate your stance on Muslims, or they will launch more attacks against America.

Last month, Trump praised Sadiq Khan for winning London’s mayoral race, and said he would be willing to create an exception in his policy restricting Muslim entry into the United States in order to allow Khan to visit. But in a statement, Khan dismissed Trump’s invitation, and also denounced his views on Islam as “ignorant,” suggesting Trump’s policies would increase the terrorist threat in both the U.S. and U.K.

“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 extremists,” he said. “Donald Trump and those around him think that Western liberal values are incompatible with mainstream Islam – London has proved him wrong.”

While Khan touted the liberal values of British Muslims, some polls have found worrying indicators that their assimilation is incomplete. A poll in April, for instance, found that two-thirds of British Muslims would not tell the government if a friend or family member became involved with extremists. Over 20 percent supported establishing sharia in the U.K.