LONDON — A senior member of Prime Minister Rishi Sunak’s government announced his resignation Tuesay night after mounting allegations that he bullied colleagues.

Gavin Williamson announced his resignation as minister of state without portfolio in letter posted on Twitter, four days after the Times of London published expletive-laden text messages he sent to another member of Parliament.

After that, a senior civil servant alleged that Williamson subjected them to sustained bullying, telling the individual to “slit your throat” on one occasion and “jump out of the window” on another.

In his resignation letter, Williamson said he had apologized for the text messages and was cooperating with an investigation of that conduct. But he rejected suggestions that the second incident involved bullying.

“I refute the characterization of these claims, but I recognize these are becoming a distraction for the good work this government is doing for the British people,” Williamson wrote. “I have therefore decided to step back from government so that I can comply fully with the complaints process that is underway and clear my name of any wrongdoing.”

Williamson’s resignation comes amid criticism that Sunak has failed to live up to his pledge to make integrity a central focus of his government. Opposition leaders have also called for the resignation of Home Secretary Suella Braverman, who Sunak reappointed just six days after she resigned for breaching the rules on ministerial conduct.

Sunak took office two weeks ago after his predecessor, Liz Truss, was forced to step down after her budget proposals triggered economic turmoil. Truss was prime minister for just six weeks after she replaced Boris Johnson, who resigned after a series of scandals ranging from illegal parties during pandemic lockdowns to allegations of improper use of political donations.

Many observers were surprised when Sunak named Williamson to a position in his government because he was twice forced out of previous Cabinet posts. Williamson resigned as defense secretary in 2019 after a leak of confidential information from the National Security Council. He lost his job as education secretary in 2021 after standardized exams were disrupted due to the pandemic.

Sunak thanked Williamson for his “unwavering support” as he accepted the resignation.

“I support your decision to step back and understand why you have taken it,” the prime minister said in a letter to Williamson.