US defense chiefs have pushed back against Donald Trump’s attempt to ban transgender people from serving in the military, saying the policy would not be overturned until they received formal direction to do so.

In a rebuke to Trump’s attempt to run the government and military via Twitter, Gen Joseph Dunford, America’s top military officer, said on Thursday that the armed forces would continue to permit transgender people to serve openly until the defense secretary, Jim Mattis, has received Trump’s “direction” to change the policy and figured out how to implement it.

In a memo to all military service chiefs, commanders and enlisted military leaders, Dunford, chairman of the joint chiefs of staff, said “there will be no modifications” to current policy for now, amid questions about Trump’s announcement on Twitter that the US government will not “accept or allow” transgender people to serve in any capacity in the military.

“I know there are questions about yesterday’s announcement,” Dunford began, adding that nothing would change until the president’s direction has been received by Mattis and Mattis has issued “implementation guidance”.

“In the meantime, we will continue to treat all of our personnel with respect,” Dunford wrote. “As importantly, given the current fight and the challenges we face, we will all remain focused on accomplishing our assigned missions.”

The Dunford statement suggests that Mattis was given no presidential direction on changing the transgender policy. Mattis has been on vacation this week and has been publicly silent amid questions about Trump’s announced ban. His spokesmen declined to comment on Thursday. On Wednesday, they said the Pentagon would work with the White House and provide revised guidance to the military “in the near future”.

Dunford himself was not aware that Trump was going to announce the ban, a US official said. The official was not authorized to discuss the matter and so spoke on condition of anonymity.

Trump’s announcement caught the Pentagon flat-footed and unable to explain what it called Trump’s “guidance”.

“Please be advised that the United States Government will not accept or allow Transgender individuals to serve in any capacity in the U.S. Military,” the commander in chief tweeted.

Trump wrote that he had consulted with “my generals and military experts”, but he did not mention Mattis, the retired Marine general who recently told the service chiefs to spend another six months weighing the costs and benefits of allowing transgender individuals to enlist. At the time, Mattis said this “does not presuppose the outcome of the review”, but Trump’s tweets appeared to have done just that.

The Pentagon has not released data on the number of transgender people currently serving. A Rand Corporation study has estimated the number at between 1,320 and 6,630 out of 1.3 million active-duty troops.

Criticism for Trump’s action was immediate and strong from both political parties.

John McCain, the Arizona Republican and Vietnam war hero, said Trump was simply wrong.

“Any American who meets current medical and readiness standards should be allowed to continue serving,” he said. “There is no reason to force service members who are able to fight, train and deploy to leave the military – regardless of their gender identity.”

Not everyone at the Capitol agreed.

Duncan Hunter, a member of the House armed services committee, said: “It’s about time that a decision is made to restore the warrior culture and allow the US military to get back to business.”

Transgender people already in uniform were concerned about what comes next.

“Everybody is hurt, everybody is scared,” said Rudy Akbarian, 26, who is in the military but did not want to identify his branch.

Trump’s sudden declaration appears to halt a decades-long trend toward more inclusive policies on military service, including the repeal in 2010 of a ban on gays serving openly. Bill Clinton began the push to allow gay people to serve in 1993. In December 2015, Barack Obama’s Pentagon chief, Ash Carter, announced that all military positions would be open to women. Liberalizing policy on transgender troops was the next step.

Just last week, when asked about the transgender issue at a Senate hearing, Gen Paul Selva, vice-chairman of the joint chiefs of staff, said: “I am an advocate of every qualified person who can meet the physical standards to serve in our uniformed services to be able to do so.”

Transgender service members have been able to serve openly since 2016, when Carter ended the ban. Since 1 October, transgender troops could receive medical care and start changing their gender identifications in the Pentagon’s personnel system.

Carter also gave the services until 1 July to develop policies to allow people already identifying as transgender to join the military if they meet normal standards and have been stable in their identified genders for 18 months.

On 30 June, Mattis extended the 1 July deadline to 1 January 2018, saying the services should study the impact on the “readiness and lethality of our forces”.

The White House press secretary, Sarah Huckabee Sanders, said Trump had made “a military decision”. She said it was his judgment that allowing transgender service “erodes military readiness and unit cohesion”.

Sanders said the “president’s national security team was part of this consultation” and that Trump “informed” Mattis of his decision immediately after he made it on Tuesday.

Asked if Trump was aware that he cannot make policy changes via Twitter, Huckabee Sanders replied: “I think he was making the announcement of the policy change. Like I said, they are going to have to work out the details on how that moves forward to lawfully implement that policy change from this point.”



