July 27 (UPI) -- The U.S. military's transgender policy will not change until President Donald Trump formally issues directions to the Pentagon, the chairman of the Joint Chiefs of Staff said Thursday.
Trump announced the policy change on Twitter, which does not count as a formal notification.
"There will be no modifications to the current policy until the president's direction has been received by the secretary of defense and the secretary has issued implementation guidance," USMC Gen. Joseph Dunford wrote in a letter to service chiefs, commanders and senior enlisted leaders.
"In the meantime, we will continue to treat all of our personnel with respect. As importantly, given the current fight and the challenges we face, we will all remain focused on accomplishing our assigned missions."
In his tweet, Trump said that he will "not allow or accept" transgender people serving in the military. The Pentagon and White House press secretary Sarah Huckabee Sanders offered no immediate direction how the policy would be implemented, including transgender persons already in the military.
Unidentified U.S. defense officials told CNN that the top military leaders across all four service branches -- Army, Navy, Marines, Air Force -- were blindsided by the president's policy announcement on Twitter.
Last month, Defense Secretary James Mattis announced a six-month review, starting July 1, to work with service chiefs and secretaries to evaluate the prospect of allowing transgender people to enlist.
A U.S. official told CNN that Mattis, who is on vacation, was consulted on Trump's plan.
The only information from Trump has come in a series of tweets.
"After consultation with my Generals and military experts, 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," Trump wrote. "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."
Conservative legislator Rep. Vicky Hartzler had proposed an amendment on the defense authorization bill to ban the Pentagon from paying for "transition surgeries," as well as hormone therapy, a Republican congressional aide familiar with the situation said.
A Republican leadership source added that Trump's announcement on a total ban was "far beyond leaders' expectations and caught many by surprise."
The cost of medical services for transgender individuals in the military was between $2.4 million and $8.4 million out of a $6.2 billion medical budget, according to a Rand Corporation study in June.
Rand researchers estimated between 1,320 and 6,630 active duty members, and between 830 and 4,160 reserve members, are transgender.
A 2014 UCLA study estimated the overall figure is 15,500.