Gavin Williamson, a cabinet office minister in Sunak's government, resigned on Tuesday after mounting allegations that he had bullied colleagues.
The Sunday Times and other local media outlets reported days ago that Williamson sent expletive-laden messages to a colleague. On Monday, the Guardian reported that he told a senior civil servant to "slit your throat" while he was defense secretary in Theresa May's government.
In his resignation letter posted on Twitter, Williamson said he had apologized to the recipient for the messages and was cooperating with an investigation of that conduct. However, he rejected claims of bullying in the second incident.
"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," he 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."
British Prime Minister Rishi Sunak said he had accepted Williamson's resignation "with great sadness."
Williamson's resignation came at a time when Sunak's choice of some of his ministers has come under intense scrutiny. Leaders of opposition parties have demanded the resignation of Home Secretary Suella Braverman, whom Sunak reappointed days after she resigned from Truss's cabinet for breaching the rules on ministerial conduct.
