US President Donald Trump says transgender individuals will not be able to serve in the country's military.
In a series of tweets, Mr Trump said he had made the decision "after consultation with my generals and military experts".
He said transgender people will not be able to serve the US military "in any capacity".
He said: "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. Thank you".
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
It was announced last year that the Pentagon would provide sex-change operations to some active-duty transgender service members if a military doctor determined that surgery is required to treat the individual's gender dysphoria.
The treatment could include behavioural health care, hormone therapy, and in some cases gender reassignment surgery.
Service members must be diagnosed as stable in their preferred gender for 18 months before they can receive treatment.
Pentagon spokesman Major Ben Sakrisson said in September 2016: "The Secretary of Defence has made clear that service members with a diagnosis from a military medical provider indicating that gender transition is medically necessary will be provided medical care and treatment for the diagnosed medical condition".
This announcement came just days after lawyers representing Chelsea Manning said the army had agreed to provide her gender-reassignment surgery.
Manning, who served time in prison for leaking classified and sensitive material to the website WikiLeaks, was recommended for the surgery by a doctor last April.
The US military has had a long and varied history with regard to sexual orientation of its members.
In 1992, then-President Bill Clinton promised to lift a ban on gays in the military.
A year later the "Don't ask, don't tell" law was passed, in which military applicants would not be asked about their sexual orientation.
In 2008, the then future President Barack Obama's campaign included a call to repeal the ban.
But it was not until 2010, following several studies into "the risk factor of homosexuality in the military", as well Republicans' repeated attempt to block the vote, that the Senate eventually voted 65-31 in favour to repeal the "Don't ask, don't tell" law.
