New British Prime Minister Andy Burnham exchanged messages with someone posing as Susie Wiles, the White House chief of staff, several media outlets reported on Monday.

According to Politico, which broke the story quoting anonymous sources, the British leader sent a “few messages” via an unspecified communication channel to a person he believed to be Wiles before becoming suspicious.

The incident was deemed serious enough for the British embassy in Washington to raise the matter with the White House, according to two sources cited by Politico.

Neither the date nor the content of the exchanges is known.

Burnham succeeded former Labour Party leader Keir Starmer as prime minister on July 20.

“We do not comment on national security matters,” a representative for Burnham’s Downing Street office said, without denying the exchanges.