A senior Australian Border Force officer is believed to have resigned while facing an investigation into his personal conduct.

Assistant Commissioner Peter Docwra was being investigated over allegations he had an inappropriate relationship with a female staff member.

Mr Docwra, who was head of the ABF’s capability division, was on leave before deciding to resign on Thursday, The Australian reports.

A spokesperson for the Immigration Department confirmed Mr Docwra was no longer an ABF employee.

“The Department does not comment or confirm whether any matter is, or is not, under investigation,” the spokesperson said.

“The Department has a robust integrity regime which has been the subject of numerous public statements, including on our website. The Secretary has also addressed the issue of integrity in opening statements at Senate Estimates.”

Reports of an inquiry into Mr Docwra’s personal conduct first surfaced last week, just days after it emerged ABF commissioner Roman Quaedvlieg was on leave due to a separate external investigation.

The investigation into Mr Quaedvlieg centres on allegations he helped a junior staffer with whom he had a relationship secure work at Sydney airport.

He is understood to have denied the allegations against him.

Australian Border Force Commissioner Roman Quaedvlieg with Immigration Minister Peter Dutton. Photo: AAP