The Department of Defense declared Thursday there will be “no modifications to the current policy” on transgender service members for now, a day after President Trump issued a surprise three-tweet directive banning those troops from the military.

In a memo to service chiefs and commanders, Chairman of the Joint Chiefs of Staff Gen. Joseph Dunford, Jr. declared no changes to the policy until "the President’s direction has been received by the Secretary of Defense and the Secretary has issued implementation guidance" -- which has not yet happened.

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

Dunford’s statement suggests Defense Secretary James Mattis wasn’t given any significant heads up on the policy change. Mattis was on vacation when Trump tweeted. Mattis has also been publicly silent amid questions about Trump’s announced ban, though the White House said Wednesday that Mattis was "immediately informed" of Trump's decision.

Dunford himself was not aware that Trump was going to announce the ban, a U.S. official said.

Trump’s Wednesday morning tweets reversed an Obama-era policy of allowing transgender troops to serve. Trump wrote:

"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. 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."

TRUMP ANNOUNCES BAN ON TRANSGENDER INDIVIDUALS SERVING IN THE MILITARY

Trump 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.

White House Press Secretary Sarah Huckabee Sanders seemed unable to provide basic details on the rollout of the change on Wednesday, saying the implementation would be worked out "lawfully."

Civil liberty and LGBTQ groups quickly condemned Trump’s decision but were left in limbo trying to decipher the tweets. Was Trump enacting new policy or simply saying what he’d like to see happen?

“If you’re a transgender service member anywhere in the world, you are very nervous about what you’re hearing,” former Army Chief Eric Fanning, the first openly gay head of a U.S. military service, told NBC's "Today" show. “Now you’re probably very confused and very frightened about what the future holds for you, when your commander in chief tweets a message like this.”

GLAAD President Sarah Kate Ellis said the president is “calling for a witch hunt & purge of 15,000 trans military Americans.”

Transgender service members have been able to serve openly in the military since last year, when former Defense Secretary Ash Carter ended the prior ban. Some lawmakers including Reps. Steve King, R-Iowa, and Duncan Hunter, R-Calif., backed the president's move.

Sanders said Trump made "a military decision." She said it was his judgment that allowing transgender service "erodes military readiness and unit cohesion."

But experts told Fox News that from a legal standpoint, Trump’s tweets for now have all the merit of a public service announcement.

In the short term, nothing changes until a policy is drafted or some type of formal modification is made to military regulations. Lawsuits cannot be filed, and transgender troops cannot be yanked out of service or denied health care benefits.

“Until formal guidance is issued, nothing is going to change,” one U.S. defense official told Fox News, adding that tweets don’t count as “formal guidance.”

Separately, the Navy announced it would continue to provide transgender individuals medical treatment.

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

Former President Bill Clinton in 1993 began the push to allow gays to serve, only under the controversial "don't ask, don't tell" policy. In December 2015, former President Barack Obama's Pentagon chief, Carter, announced that all military positions would be open to women.

Liberalizing policy on transgender troops was the next step. Carter also gave the services until July 1 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 June 30, Mattis extended the July 1 deadline to next Jan. 1, saying the services should study the impact on the "readiness and lethality of our forces."

Fox News' Lucas Tomlinson and The Associated Press contributed to this report.