WASHINGTON -- The White House will soon provide the Pentagon official guidance implementing a new ban on transgender servicemembers in an order expected to grant Defense Secretary Jim Mattis authority to discharge non-deployable transgender troops, according to news reports.

A White House memorandum, expected to be sent to the Defense Department within days, directs the Pentagon to deny transgender men and women entry into the military and to cease paying for medical treatments for current transgender servicemembers, the Wall Street Journal reported late Wednesday, citing unnamed U.S. officials familiar with the 2 1/2-page memo.

Mattis would be given six months to fully implement the new policy, according to the New York Times, which wrote the memo has not been finalized.

Pentagon and White House officials declined Thursday to confirm the order's existence. A Pentagon spokesman said the Defense Department had yet to receive official guidance about the new ban on transgender servicemembers that President Donald Trump abruptly announced last month via Twitter.

"At this time, [the Defense Department] has not received formal guidance from the White House as a follow-up to the commander in chief's announcement on military service by transgender personnel," said Army Lt. Col. Paul Haverstick, a Pentagon spokesman.

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Trump's July 27 three-tweet announcement that transgender people would no longer be allowed to serve "in any capacity" caught Pentagon officials off guard. Top military leaders, including Marine Gen. Joseph Dunford, the chairman of the Joint Chiefs of Staff, quickly announced no changes would be immediately implemented.

The president cited "tremendous medical costs and disruption" to military units in defending his decision to ban transgender servicemembers, who were only granted the right to serve openly by former President Barack Obama's administration in June 2016.

The order appears to give Mattis leeway in determining whether transgender servicemembers should be dismissed. The defense secretary would be only required to remove troops who were deemed unable to deploy into a combat, training or other assignments for medical reasons related to gender dysphoria, a medical condition attributed to transgender people and recognized by the American Psychiatric Association.

Trump's social media announcement in July was met with immediate condemnation from Democratic and Republican lawmakers, including Republican Sen. John McCain, the chairman of the Senate Armed Services Committee, who said all capable people should be allowed to serve.

The new order was quickly admonished by lesbian, gay, bisexual and transgender advocacy groups following the Wall Street Journal report.

"Despite the overwhelming bipartisan condemnation of his reckless tweets, President Trump is still pushing forward with his vicious assault on transgender service members," said Ashley Broadway-Mack, the president of the American Military Partner association, which advocates for LGBT troops. "His foolhardy assertion that transgender servicemembers are not able to deploy is simply not rooted in fact. Transgender servicemembers are just as deployable as any other servicemember."

Aaron Belkin, the director of the Palm Center, a research organization which helped the Pentagon shape policy on allowing transgender people to serve openly, called Trump's ban "unconscionable" and accused the president of implementing it for "political reasons."

"Transgender troops have been serving openly in the U.S. military for more than a year, and have been widely praised by commanders," Belkin said. "Imposing one set of standards for transgender troops, and another set of standards for everyone else is a recipe for disruption, distraction and waste."

It remains unclear how many transgender people are openly serving in the military. Pentagon officials have declined to provide a specific number, saying there are "hundreds" of servicemembers who have identified themselves as transgender individuals. The Defense Department has declined to release specific information about how many troops are now receiving medical treatment – such as hormone therapy or gender-reassignment surgery – for gender dysphoria.

A Rand Corp. study commissioned last year by the Pentagon to help it determine its transgender policy estimated there were between 1,320 and 6,630 transgender people among about 1.3 million active-duty troops.

Five transgender servicemembers filed a lawsuit in the U.S. District Court for the District of Columbia against Trump and top Pentagon officials earlier this month challenging the new ban. The servicemembers, who were only identified as "Jane Doe" Nos. 1-5, argued the ban would violate the equal protection component of the Fifth Amendment to the Constitution and their right to due process.

"Execution of the president's directive will result in an end to service by openly transgender servicemembers and has already resulted in immediate, concrete injury to plaintiffs by unsettling and destabilizing plaintiffs' reasonable expectation of continued service," the lawsuit stated.