WASHINGTON, March 23 (Xinhua) -- U.S. President Donald Trump signed a memorandum on Friday that bans most transgender troops from military service, but gives discretion to the armed forces in implementing the policies.x The accession or retention of individuals "with a history or diagnosis of gender dysphoria" -- those who may require substantial medical treatment -- "presents considerable risk to military effectiveness and lethality," said a statement released by the White House late Friday.

They are "disqualified from military service except under certain limited circumstances," according to the memo.

"The Secretary of Defense, and the Secretary of Homeland Security, with respect to the U.S. Coast Guard, may exercise their authority to implement any appropriate policies concerning military service by transgender individuals," it added.