Washington (AFP) - President Donald Trump's administration has asked a federal court to block the Pentagon from starting the hiring of transgender recruits next year.

The filing by the Justice Department late on Wednesday is the latest in a series of legal measures that have unfolded since Trump sent out three tweets in July saying that transgender troops could not serve "in any capacity" in the military.

Those tweets, later followed by a formal White House memorandum, set off a roar of protest -- with several service members and rights groups quick to sue.

Two federal courts have since temporarily blocked Trump's ban, and the Pentagon was due to start accepting transgender recruits on January 1.

The government's filing calls for a partial delay, specifically that the Pentagon does not accept transgender recruits from that date.

"Defendants request that the court stay the portion of its preliminary injunction requiring defendants to begin accessing transgender individuals into the military on January 1, 2018," pending an appeal decision, court documents state.

The Pentagon declined to comment on the litigation.

Under a new policy announced last year by the Obama administration, the Pentagon was originally supposed to start accepting transgender recruits on July 1, 2017.

However, that was delayed for six months by Defense Secretary Jim Mattis pending further review of the matter.

"Compelling the military to implement a new accessions policy while it is simultaneously completing a comprehensive study of military service by transgender individuals ... would waste significant military resources and sow unnecessary confusion," the government argued in its filing.