The British prime minister, Andy Burnham, exchanged brief text messages with a person he thought was President Trump’s chief of staff, Susie Wiles, a government official said on Monday.

Mr. Burnham quickly grew suspicious and reported the interaction to security authorities, the official added.

It was unclear when the exchanges took place. A spokeswoman for Mr. Burnham declined to comment publicly, citing a longstanding policy not to comment about national security issues.

But the government official, who declined to be identified because of the security policy, said the prime minister had exchanged a few messages of no significance with someone claiming to be Ms. Wiles, Mr. Trump’s top White House aide.

The official declined to provide details about the text messages, which were first reported by Politico, or to say which security agency Mr. Burnham had reported them to.

Ms. Wiles is one of Mr. Trump’s closest advisers. She comanaged his 2024 presidential campaign and has been running his White House staff since he returned to office in 2025.

Last year, The Wall Street Journal reported that senators, governors and some business leaders had received phone calls or text messages from someone claiming to be Ms. Wiles, and that Ms. Wiles had said contacts on a personal cellphone of hers had been hacked. The Journal said at the time that federal officials were investigating.

In 2024, David Cameron, then the British foreign secretary, had a video call and exchanged several text messages with someone pretending to be Petro Poroshenko, a former president of Ukraine.

As foreign secretary in 2018, Boris Johnson had an 18-minute phone call with someone claiming to be the prime minister of Armenia. According to audio that was later released, the pair talked about Vladimir Putin and about the poisoning of Sergei Skripal, a Russian double agent, in Salisbury, England.