U.K. Prime Minister Theresa May fired her Defense Secretary on Wednesday after concluding that he was involved in leaking details about a possible arrangement with Chinese telecoms giant Huawei to the media.

“The Prime Minister has this evening asked Gavin Williamson to leave the Government, having lost confidence in his ability to serve in the role of Defense Secretary and as a member of her Cabinet,” 10 Downing Street said in a statement.

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“The Prime Minister’s decision has been informed by his conduct surrounding an investigation into the circumstances of the unauthorized disclosure of information from a meeting of the National Security Council,” the statement said.

Penny Mordaunt, the International Development Minister, was named as Williamson's replacement and approved by the Queen, according to Downing Street. She becomes the first woman to hold the position.

Williamson's sacking came after an investigation into a leak to The Daily Telegraph -- which reported that the National Security Council, chaired by May, had agreed to allow Huawei to help build Britain’s new 5G network.

The Telegraph reported that greenlighting Huawei’s involvement was likely to anger the U.S., which has banned Huawei from its government networks and has urged its allies to do the same amid concerns the Chinese could use Huawei’s equipment to spy and hack into government systems.

Theresa May fired Defence Secretary Gavin Williamson on Wednesday. (AP)

After the leak, May ordered an investigation into the leak and, in a letter to Williamson, said she had been “concerned by the manner in which you have engaged with this investigation.”

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She said that she had put to him information “which provides compelling evidence suggesting your responsibility for the unauthorized disclosure.”

“No other, credible version of events to explain this leak has been identified,” she said.

Williamson told the BBC that he still denies he was the source of the leak to the National Security Council.

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The controversy comes at a difficult time for May, where she is facing significant rebellion within her own Conservative Party and Cabinet over her handling of Britain’s departure from the European Union -- which has been delayed to as late as October.

Voters will go the polls on Thursday for local elections and in European Parliament elections later this month, where May’s party is expected to lose seats in both.