WASHINGTON — A federal judge on Monday blocked a White House policy barring military service by transgender troops, noting that the policy did not appear to be based on facts, but instead on “a desire to express disapproval of transgender people generally.’’

President Trump announced in a series of tweets in July that US forces could not afford the “tremendous medical costs and disruption’’ of transgender troops and said “the United States Government will not accept or allow transgender individuals to serve in any capacity in the U.S. Military.’’

A presidential memo released in August required all transgender service members to be discharged by March.

Transgender groups sued in August on behalf of transgender service members, arguing the ban was discriminatory and violated their constitutional right to due process and equal protection under the law.

On Monday, Judge Colleen Kollar-Kotelly of the US District Court for the District of Columbia issued an injunction blocking enforcement of the ban until the case is resolved, saying the effect of the order was to revert to the status quo.

The judge, named to the court by former president Bill Clinton, noted the changes in policy were “not genuinely based on legitimate concerns regarding military effectiveness or budget constraints, but are instead driven by a desire to express disapproval of transgender people generally.’’

The ruling allows transgender troops to join the military and to reenlist, pending the outcome of the case, but leaves in place a White House provision that prohibits federal spending on sex reassignment surgery for troops.

Supporters of transgender troops noted the injunction was temporary, but were optimistic.

“The court has clearly recognized the Trump administration is discriminating. We hope this is the beginning of the whole policy being overturned,’’ said Matt Thorn, executive director of the advocacy group OutServe.

‘‘We are enormously relieved for our plaintiffs and other transgender service members,’’ said Shannon Minter of the National Center for Lesbian Rights, an attorney handling the lawsuit. ‘‘Their lives have been devastated since Trump first tweeted he was reinstating the ban,’’ Minter said. ‘‘They are now able to serve on equal terms with everyone else.’’

White House spokeswoman Sarah Huckabee Sanders said the Justice Department was still reviewing the ruling.

Conservatives have pushed to curtail transgender policies since a longstanding ban on transgender troops was lifted in 2016. In June, some Republicans in Congress unsuccessfully sought to ban sex-reassignment surgery by attaching it to the military spending bill.

A few weeks later, when Trump announced his policy on Twitter, he went further, banning transgender service members entirely. Top military officials were caught off guard, and many were reportedly dismayed by the new policy.

In a separate development Monday, senior national security officials told Congress a new war-powers authorization is ‘‘not legally required’’ to conduct combat operations against terrorist groups.

Secretary of State Rex Tillerson and Defense Secretary Jim Mattis testified before the Senate Foreign Relations Committee, three months after they informed the panel a post-Sept. 11, 2001, law gave the military ample authority to fight terrorist groups and a new one was unnecessary. A separate authorization for the war in Iraq, approved by Congress in 2002, remains in force.

Tillerson and Mattis say that if Congress does pursue a new authorization for foes such as the Islamic State group, it’s imperative that the existing law not be rescinded until the new one is fully in place.

A deadly ambush in Niger that killed four US service members ignited a push among many lawmakers to update the legal parameters for combat.

Several Republicans and Democrats were surprised by the depth of the US commitment in Niger and other parts of Africa. They have argued the dynamics of the battlefield have shifted over the past 16 years and it’s past time to replace the post-Sept. 11 authorization to fight Al Qaeda with a law that reflects current threats.

Senator Chris Coons, Democrat of Delaware, said on CNN that most members of Congress weren’t even in office when the authorization for the use of military force was signed into law by President George W. Bush.

Coons said it would have been difficult to imagine at the time that US soldiers would be killed in Africa by Islamic State militants based on an attack launched in 2001.

Senator Tim Kaine, Democrat of Virginia, said last week that most Americans would be surprised by the extent of the operations in Africa. Kaine and Senator Jeff Flake, Republican of Arizona, are sponsoring legislation to install a new war authority for operations against the Islamic State group, Al Qaeda, and the Taliban.

Tillerson emphasized that any new authorization, like the existing one, should not have any geographic or time restrictions placed on the use of force.

Roughly 800 US service members are in Niger as part of a French-led mission to defeat the extremists in West Africa. There are hundreds more American forces in other African countries. US troops also are battling the Islamic State in Syria.

Trump also has approved a troop increase in Afghanistan, the site of America’s longest war, and the United States is backing a Saudi Arabia-led coalition that’s carrying out airstrikes in Yemen.