London's Metropolitan Police said Friday they are opening an investigation into the leaking of ambassador Kim Darroch's communications that were critical of President Trump. Darroch resigned on Wednesday, saying the "current situation" has made it "impossible for me to carry out my role as I would like."

Met police assistant commissioner Neil Basu said in a Friday statement that there was sufficient evidence there had been "damage caused to U.K. international relations, and there would be clear public interest in bringing the person or people responsible to justice."

Basu also said that publishing the communications could be considered a crime.

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The leaked communications were originally published in Britain's Mail on Sunday. The U.K. foreign office has said it was not hack, and Downing Street said there is no evidence to suggest the involvement of foreign power, BBC News reported.

British Ambassador Kim Darroch speaks at the British Embassy to mark the U.S. Presidential Inauguration on January 18, 2017 in Washington, D.C. Paul Morigi / Getty Images

In the leaked communication, Darroch wrote, "we don't really believe this administration is going to become substantially more normal; less dysfunctional; less unpredictable; less faction-riven; less diplomatically clumsy and inept."

Darroch said that to communicate effectively with Mr. Trump, "you need to make your points simple, even blunt."

The published documents included the ambassador calling the Trump administration's policies on Iran "incoherent," saying the U.S. president might be indebted to "dodgy Russians," and raising doubts about whether the Trump White House "will ever look competent."

But Darroch has had a close relationship with numerous Trump administration officials. The president's advisers have been frequent guests at British Embassy events.

Prime Minister Theresa May initially said Darroch's still had her support, causing Mr. Trump to lash out on Twitter, calling Darroch "wacky" and a "pompous fool."

"The wacky Ambassador that the U.K. foisted upon the United States is not someone we are thrilled with, a very stupid guy," Mr. Trump wrote in one tweet.

Darroch, meanwhile, has been accused by some Brexit-backing U.K. politicians of lacking enthusiasm for Britain's departure from the European Union. The journalist who reported the leak, Isabel Oakeshott, is a strong Brexit backer and an ally of Brexit Party leader Nigel Farage, who also is Britain's leading champion of Mr. Trump.

Mr. Trump once said Farage would "do a great job" as ambassador to the United States. Farage sidestepped the idea Monday, saying "I'm not a diplomat."