WASHINGTON — Questions about the science behind gender dysphoria prompted the Pentagon's six-month delay in a new policy allowing the enlistment of transgender individuals into the military, the Joint Chiefs vice chairman told senators on Tuesday.

But outside advocates labeled that statement "willful ignorance" about the condition and a deliberate political attempt to slow down the process of allowing transgender recruits access into the ranks.

The Pentagon was scheduled to allow transgender recruits to enter the armed forces starting July 1, under a policy put in place during President Barack Obama's tenure. But on June 30, Defense Secretary James Mattis postponed the move and ordered a six-months policy review "to evaluate more carefully the impact of such accessions on readiness and lethality."

During a Senate Armed Services Committee hearing on Tuesday, Air Force Gen. Paul Selva insisted the move was not made to discriminate against transgender individuals.

"I am an advocate of every qualified person who can meet the physical standards to serve in our uniformed services to be able to do so," he said. "Our decision to delay the accessions … was largely based on a disagreement on the science of how mental health care and hormone therapy for transgender individuals would help solve the medical issues that are associated with gender dysphoria."

Mattis delays transgender military recruitment

He also added that service chiefs expressed concerns about "a host of other issues that involve the potential physical standards" of the new recruits.

"The service chiefs asked for additional time to assess so that they can make their necessary changes to infrastructure, as well as training curriculum for our basic trainees who come in in transgender status, particularly those who have not undergone gender reassignment surgery," he said.

The delay has drawn praise from conservative advocates and criticism from liberal lawmakers, who have compared it to past military policies excluding gays and minorities from enlisting.

Aaron Belkin, director of The Palm Center — which specializes in research on sexual minorities in the military — blasted Selva’s remarks about health concerns of transgender recruits as disingenuous.

"There is no scientific dispute," he said. "This is the same disturbing statements we heard about gays and lesbians during the ‘don’t ask, don’t tell’ debate. There is a global medical consensus that transition care is safe and effective.

"This is worse than foot-dragging by the service chiefs. This is ignoring science for a political agenda."

Gender dysphoria — also known as gender identity disorder — is defined by the American Psychiatric Association as "a conflict between a person's physical or assigned gender and the gender with which they identify." The Pentagon announced last year it would not only allow transgender troops to serve openly, but also pay for gender reassignment surgery for individuals dealing with the condition.

Last week, House lawmakers narrowly defeated a measure that would have blocked military officials from paying for the treatments.

The Pentagon policy delay only affects new enlistees from entering the armed forces. Transgender troops already serving are not required to conceal their gender preferences or leave the ranks because of the delay.

Both Mattis and Selva said the six-month review is still ongoing, and no long-term decisions about the policy changes have been decided yet.

Leo Shane III covers Congress, Veterans Affairs and the White House for Military Times. He can be reached at lshane@militarytimes.com.