British Prime Minister Theresa May complained directly to President Trump, after he wrote on Twitter that the people behind the Friday terrorist attack in London were known to Scotland Yard, according to a U.K. government official familiar with the conversation.

U.S. president called the British prime minister to offer his condolences over the attack on a subway train, which injured more than 20 people.

May told the U.S. leader she was unhappy with his initial response, the official said on condition of anonymity.

This isn’t the first time May has protested to Trump. Earlier this year, the premier was in a political and diplomatic bind after U.S. media reported leaked details of a British police investigation into the Manchester bomb attack that killed 20 people.