Transgender service members will be separated from the US military unless they receive an exemption, according to a Pentagon memo filed in court on Wednesday, essentially banning them from joining or serving in the military.

The move, which goes further than restrictions President Donald Trump placed on transgender service members during his first administration, was described as unprecedented by advocates.

Trump signed an executive order last month that took aim at transgender troops in a personal way — at one point saying that a man identifying as a woman was “not consistent with the humility and selflessness required of a service member.”

This month, the Pentagon had said that the US military will no longer allow transgender individuals to join and will stop performing or facilitating procedures associated with gender transition for service members.

Wednesday’s late-evening memo expands the ban to currently serving members of the military.

The memo said that the Pentagon must create a procedure to identify troops who are transgender within 30 days and then within 30 days of that, must start to discharge them from the military.

“It is the policy of the United States Government to establish high standards for service member readiness, lethality, cohesion, honesty, humility, uniformity, and integrity,” said the memo, dated February 26.

“This policy is inconsistent with the medical, surgical, and mental health constraints on individuals with gender dysphoria or who have a current diagnosis or history of, or exhibit symptoms consistent with, gender dysphoria,” it added.

There is no requirement for transgender troops to self-identify and the Pentagon doesn’t have a precise number.

The Pentagon said waivers would be granted only “provided there is a compelling government interest in retaining the service member that directly supports warfighting capabilities.”

It added that for a waiver, troops must also be able to meet a number of criteria, including that the service member “demonstrates 36 consecutive months of stability in the service member’s sex without clinically significant distress.”

During his first term, Trump announced that he would ban transgender people from serving in the military. He didn’t fully follow through, freezing their recruitment while allowing serving personnel to remain.

“The scope and severity of this ban is unprecedented. It is a complete purge of all transgender individuals from military service,” said Shannon Minter of the National Centre For Lesbian Rights (NCLR).

The memo was filed in court as part of a lawsuit brought by NCLR and GLAD Law. The suit challenges the constitutionality of the January executive order and argues that it violates the equal protection component of the Fifth Amendment.

This month, US Defence Secretary Pete Hegseth had said people with gender dysphoria already in the military would be “treated with dignity and respect.”

The military has about 1.3 million active-duty personnel, according to Department of Defence data. Although transgender rights advocates say there are as many as 15,000 transgender service members, officials say the number is in the low thousands.

A poll from Gallup published this month said 58 per cent of Americans favoured allowing openly transgender individuals serving in the military, but the support had declined from 71pc in 2019.