(CNN) Secretary of Defense Jim Mattis said Monday that the White House had still not provided policy guidance on transgender persons serving in the military, adding that they were still studying the issue, raising the prospect that transgender service members may be allowed to continue to serve despite President Donald Trump's July announcement of a ban via twitter.

"We are going to study the issue," Mattis told reporters at the Pentagon.

"The policy is going to address whether or not transgenders can serve under what conditions, what medical support they require, how much time would they be perhaps non-deployable leaving others to pick up their share of everything. There's a host of issues and I'm learning more about this than I ever thought I would and it's obviously very complex to include the privacy issues which we respect," Mattis said.

"I am waiting right now to get the President's guidance in and that I expect to be very soon," he added.

Trump announced his plan to ban transgender service members on Twitter last month. The move took the Joint Chiefs of Staff by surprise, and the Pentagon has said it is awaiting an official order from Trump before making a policy change.

The White House has yet to send official guidance to the Pentagon on the ban.

Mattis was unwilling to publicly support a 2016 Rand Corp. study commissioned by the Defense Department that put the number of transgender people in the military at between 1,320 and 6,630.

Mattis added that the guidance Chairman of the Joint Chiefs of Staff General Joseph Dunford issued still stands. In a July memo, Dunford informed service members that 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 guidelines." "In the meantime, we will continue to treat all of our personnel with respect," Dunford wrote in a memo to the military that was obtained by CNN.

Mattis said the Defense Department is working with the Trump White House: "I got my people over there in the room to give them any military background that they might need to inform them but they write their own policy of course. So we are in a supporting role right now and soon we'll have, you know, the actual direction."

Last week, five active-duty transgender service members filed a lawsuit against Trump's Twitter directive, arguing it was unconstitutional.

Asked about the ban on August 10, Trump said he was doing the military "a great favor."

"I think I'm doing a lot of people a favor by coming out and just saying it," Trump said. "As you know it's been a very complicated issue for the military, it's been a very confusing issue for the military and I think I'm doing the military a great favor."