LONDON — Prime Minister Theresa May of Britain on Wednesday abruptly fired her defense secretary, Gavin Williamson, blaming him for a leak that suggested she would give a role in designing a British telecommunications network to a Chinese company considered a security risk by the United States.

Mrs. May’s announcement was made after an investigation into a report in The Daily Telegraph about discussions in Britain’s National Security Council, of which Mr. Williamson was a member, and where secrecy is meant to be strictly observed.

The report suggested that Mrs. May had overruled objections from some senior council members, including Mr. Williamson, about allowing the Chinese company, Huawei, to build some elements of the next-generation cellular data network known as 5G.

The government later said no decision had yet been made.

But the leak provoked a negative reaction from the United States, which has been on a campaign to pressure other countries to bar Huawei from building 5G networks, saying its equipment is vulnerable to Chinese state espionage, an assertion the company denies.