Top Biden administration officials indicated Tuesday they would soon provide long-awaited details regarding the number of Americans still stranded in Afghanistan amid mounting bipartisan pressure to ensure that no American is left behind following the Taliban’s takeover.

While the Pentagon said about 4,000 American passport holders and their families have been evacuated during chaotic rescue operations, the White House has yet to reveal exactly how many Americans have been unable to leave. With President Biden’s Aug. 31 deadline just days away, administration officials have a "political incentive" to keep details vague, according to Nathan Sales, a former ambassador-at-large and counterterrorism coordinator at the U.S. State Department.

"I think the administration sees a real political vulnerability because the message ‘leave no person behind, leave no American behind’ is one that really resonates with the American people," Sales, now a senior fellow at the Atlantic Council, told Fox News. "The smaller the denominator is, the less exposure they have to being criticized for failing to effectively evacuate vulnerable Americans."

BIDEN: US WITHDRAWAL CONTINGENT ON TALIBAN'S COOPERATION

The White House has faced mounting criticism over its failure to provide a precise figure. Several top administration officials, including Pentagon spokesman John Kirby and national security adviser Jake Sullivan, have said they did not know the number.

Biden addressed concerns about the ambiguity during his speech from the White House. 

"I’ve asked Sec. Blinken to give you an update and a detailed report on exactly how many Americans are still in Afghanistan, how many have gotten out and what our projection is," Biden said.

The president said U.S. officials have evacuated 70,700 people since Aug. 14 and were "on a pace" to meet his Aug. 31 deadline – an assertion disputed by some within his own party. Earlier this week, House Intelligence Committee Chairman Adam Schiff, D-Calif., said it was "very unlikely" the U.S. would be able to complete its evacuation operations by Aug. 31.

The administration’s failure to provide more details about Americans on the ground in Kabul has exacerbated concerns that some could be left behind amid a chaotic withdrawal. The Taliban has reportedly hindered some would-be evacuees from reaching the airport and the group’s representatives say they will support "no extensions" beyond Biden’s Aug. 31 withdrawal date.

Psaki pushed back on criticism after Fox News’ Peter Doocy noted at her Tuesday press briefing that some Americans had been unable to reach U.S. officials regarding their evacuation. She reiterated that the Biden administration was "committed to bringing Americans home who want to leave," adding that U.S. officials were making round-the-clock efforts to contact Americans known to still be in the country.

"Just to remind you, the U.S. government does not track our citizens when they travel around the world," Psaki said. "We rely on self-reporting, not just in Afghanistan, anywhere in the world. People have to decide to register or not. It's up to them, individuals, whether they decide to register or not, wherever they may be."

CLICK HERE TO GET THE FOX NEWS APP

The State Department will provide an "exact number" on Wednesday, Psaki added.

But verifying the exact number of Americans who require evacuation will prove difficult, given the fragile conditions in Kabul and limited U.S. capabilities on the ground. 

"I think they don’t really have a good bead on what the number is," Sales said. "In the chaos that has unfolded because of the administration’s imperfect execution of the withdrawal, I think it’s just very, very difficult for them to keep tabs on everyone who’s there. My guess would be that we continue to see imprecise numbers and ambiguity coming out of the State Department."