US president Donald Trump is barring transgender people from serving in the military “in any capacity,” citing “tremendous medical costs and disruption.”

Mr Trump’s announcement on Wednesday morning (11pm AEST) on Twitter did not say what would happen to transgender people already in the military.

The president tweeted that after consulting with “Generals and military experts,” the government “will not accept or allow Transgender individuals to serve in any capacity in the US. Military.” “Our military must be focused on decisive and overwhelming victory and cannot be burdened with the tremendous medical costs and disruption that transgender in the military would entail,” he added.

After consultation with my Generals and military experts, please be advised that the United States Government will not accept or allow...... — Donald J. Trump (@realDonaldTrump) July 26, 2017

....Transgender individuals to serve in any capacity in the U.S. Military. Our military must be focused on decisive and overwhelming..... — Donald J. Trump (@realDonaldTrump) July 26, 2017

....victory and cannot be burdened with the tremendous medical costs and disruption that transgender in the military would entail. Thank you — Donald J. Trump (@realDonaldTrump) July 26, 2017

Trans advocate Caitlyn Jenner lashed out at Mr Trump following his ban of transgender men and women from serving in the military.

“There are 15,000 patriotic transgender Americans in the US military fighting for all of us. What happened to your promise to fight for them?” she asked in response to Mr Trump’s June 2016 tweet where he promised the LGBT community, “I will fight for you while Hillary brings in more people that will threaten your freedoms and beliefs.”

Jenner’s response, along with celebrities such as Mia Farrow, George Takei, Sandra Bernhard and Laverne Cox, came hours after the announcement from President Trump that transgender people would not be serving in the US armed forces.

Though Jenner is a longtime Republican, this is not the first time she has spoken out against decisions made by the Trump administration. In February, she called the choice to revoke guidelines on transgender use of bathrooms in public schools a “disaster.”

Already, there are as many as 250 service members in the process of transitioning to their preferred genders or who have been approved to formally change gender within the Pentagon’s personnel system, according to several defence officials.

There are 15,000 patriotic transgender Americans in the US military fighting for all of us. What happened to your promise to fight for them? https://t.co/WzjypVC8Sr — Caitlyn Jenner (@Caitlyn_Jenner) July 26, 2017

My fellow trans Americans despite what some may say your existence is valuable. Your lives, safety, & service matter. #TransIsBeautiful — Laverne Cox (@Lavernecox) July 26, 2017

To all the trans folks currently serving in the military thank you for your service. I am sorry your "commander in chief" doesn't value it. — Laverne Cox (@Lavernecox) July 26, 2017

Marginalized folks have often found ourselves at odds with systems which seek to subjugate & erase us. Let us love each other more & fight — Laverne Cox (@Lavernecox) July 26, 2017

Transgender service members have been able to serve openly in the military since last year, when former Defense Secretary Ash Carter ended the ban. Since October 1, transgender soldiers have been able to receive medical care and start formally changing their gender identifications in the Pentagon’s personnel system.

But Mr Carter also gave the services until July 1 to develop policies to allow people already identifying as transgender to newly join the military, if they meet physical, medical and other standards, and have been stable in their identified genders for 18 months. Military chiefs recently announced a delay on allowing transgender people from enlisting.

Key concerns include whether currently enlisted troops have had medical or other issues that cause delays or problems with their ability to deploy or meet physical or other standards for their jobs.

Military leaders also want to review how transgender troops are treated, if they’re discriminated against or if they have had disciplinary problems, the officials said. They were not authorised to discuss internal deliberations publicly so spoke on condition of anonymity.

In late June, Pentagon chief Jim Mattis had delayed for six months a plan put in place under Barack Obama’s administration to start accepting transgender recruits.

An estimated 2500 to 7000 transgender people are among the 1.3 million active duty service members.

TENSIONS STAYING PUT

Secretary of State Rex Tillerson is knocking down a flurry of speculation that he is unhappy in his job and may soon quit.

Asked about the resignation rumours on Wednesday, Tillerson told reporters at the State Department that “I’m not going anywhere.”

He said he would remain as the nation’s top diplomat “as long as the president lets me.”

Asked about his relationship with President Donald Trump, Tillerson replied: “It’s good.” Washington has been buzzing with rumours since the beginning of the week that Tillerson will soon leave his post due to frustration with Trump and others in the White House.

The State Department had previously denied them but Wednesday marked the first time that Tillerson has addressed them directly.

SESSIONS STILL UNDER FIRE

Elsewhere, Mr Trump isn’t letting up on his Twitter criticism of Attorney-General Jeff Sessions.

Mr Trump tweeted to complain about why Mr Sessions didn’t replace the acting FBI director, Andrew McCabe.

But it’s up to the president to hire — and fire — the bureau’s chief.

The president says McCabe was “in charge” of the FBI’s Hillary Clinton email investigation, but “got big dollars (US$700,000, AU$874,000) for his wife’s political run from Hillary Clinton and her representatives.”

Are you TRYING to be an asshole? https://t.co/QW9axAScmO — Andy Cohen (@Andy) July 26, 2017

Certainly every person currently serving in our armed forces exemplifies these qualities. Thank you LGBT of the military, Air Force & Navy. https://t.co/DjifxI3dDc — zoe kazan (@zoeinthecities) July 26, 2017

Donald: With your ban on trans people from the military, you are on notice that you just pissed off the wrong community. You will regret it. — George Takei (@GeorgeTakei) July 26, 2017

no. My God. This must be challenged. https://t.co/H9DBE4cmK7 — Mia Farrow (@MiaFarrow) July 26, 2017

@Caitlyn_Jenner wake up sweetheart give Your wonderful president a call & discuss #noTransgender in military congrats on a great choice! — Sandra Bernhard (@SandraBernhard) July 26, 2017

I grew up in a military w/ LGBT people serving in the shadows. We can't let DT turn back the clock on our brave, trans soldiers. #RISEUP — Dustin Lance Black (@DLanceBlack) July 26, 2017

The Associated Press reported that Mr Trump misstated facts about Mr McCabe.

Mr McCabe’s wife ran for the Virginia Senate in 2015 and received donations from Democratic Governor Terry McAuliffe, a Clinton friend and ally.

Those donations also happened before the FBI says Mr McCabe was promoted to deputy director of the FBI and took a supervisory role in the email investigation.

Why didn't A.G. Sessions replace Acting FBI Director Andrew McCabe, a Comey friend who was in charge of Clinton investigation but got.... — Donald J. Trump (@realDonaldTrump) July 26, 2017

...big dollars ($700,000) for his wife's political run from Hillary Clinton and her representatives. Drain the Swamp! — Donald J. Trump (@realDonaldTrump) July 26, 2017

Mr McCabe became acting director in May after Mr Trump fired FBI head James Comey.

“Why didn’t AG Sessions replace Acting FBI Director Andrew McCabe, a Comey friend who was in charge of Clinton investigation but got big dollars ($700,000) for his wife’s political run from Hillary Clinton and her representatives. Drain the Swamp!” Mr Trump tweeted.