At least 250,000 Afghans who may be eligible for expedited U.S. visas remain in Afghanistan, far too many for U.S. forces to rescue before their deadline to leave next week, new estimates suggest.

A suicide attack that killed dozens of people outside Kabul’s airport Thursday seriously threatened the evacuation effort and called into question whether any additional people would be allowed inside the airport.

But even if U.S. forces had continued the previous pace of up to 20,000 evacuations a day, the estimates suggest the effort was not coming close to rescuing the full group of Afghans who may be eligible to leave before President Joe Biden’s deadline to depart, Aug. 31.

Many Afghan interpreters, advisers and others who worked with the U.S. government or U.S. organizations over the past 20 years and their families are eligible for special visas. And many fear retribution from the Taliban and are desperate to leave.

But precise figures are impossible, as U.S. officials have not said how many remain in the country.

The estimates are based on reports on Afghan employment published yearly by the Department of Defense and analyzed by the Association of Wartime Allies, a group that advocates for Afghans affiliated with the U.S., and researchers at American University. Other estimates vary widely, from 100,000 to over 300,000 people.

The group estimated that the number could be far higher, depending on the assumptions used: More than 1 million Afghans who remain in the country, it found, could be eligible for expedited immigration status.

U.S. officials said Thursday that 95,700 people, including Americans, Afghans and others, had been flown out of Kabul since the government fell to Taliban forces on Aug. 14.

To make the estimates, the researchers reviewed Department of Defense employment reports and estimated how many employees filled jobs that were eligible for visas and how long they worked. They then estimated the size of their immediate families and subtracted how many may have already left the country.

They include Afghans eligible for two visa programs. Special Immigrant Visas are available to those who worked with the U.S. military and U.S. Embassy as interpreters, translators, advisers and in other jobs during the war. And Priority 2 visas are available to those who worked for U.S. organizations and projects supported by the U.S. government.

The figures do not include many more Afghans who are not eligible for visas but could be at risk from the Taliban because of their roles in the Afghan government or military, or because they are activists or religious minorities. On Tuesday, White House press secretary Jen Psaki estimated that broader number could also be in the millions.

The International Rescue Committee has estimated that over 300,000 Afghan civilians have been affiliated with the U.S. mission. One administration official said earlier this week that the number of people who needed to be evacuated could be more than 100,000.

On Tuesday, before the suicide attack at the airport, Biden reaffirmed his plan to remove all U.S. troops by the end of the month, although he said the timeline could be adjusted if necessary. “We’re currently on a pace to finish by Aug. 31,” he said.

But other senior U.S. officials doubt the evacuations will be complete by then. The number of potentially eligible Afghans is far higher than the number of Americans, who officials have said are their first priority. At least 4,500 U.S. citizens and their family members have been evacuated, and roughly 1,500 U.S. citizens remain, Secretary of State Antony Blinken said Wednesday.

Blinken said that the United States would evacuate as many Afghan allies as possible, and that any Americans or Afghans who have worked with the U.S. mission and want to leave after that date should be free to do so. The Taliban have promised to allow “free passage” to those who qualify even after the withdrawal, he said. “That effort will continue every day,” he said.

But the evacuation mission is widely expected to slow to a trickle once the U.S. military exits.

Despite their promises, the Taliban said they would block Afghans trying to leave the country from traveling to Kabul’s airport on Tuesday. Even with the Americans still operating the airport, the obstacles for anybody trying to evacuate are immense. Just getting there is a perilous ordeal, with jostling, desperate crowds braving Taliban checkpoints, clogging the roads and risking injury or death.

And some Afghan military interpreters and other close U.S. allies were being turned away at the airport by U.S. officials in order to give priority to U.S. citizens and green card holders, a State Department official said Monday.

One woman who worked for the U.S. Agency for International Development described being removed from the airport by U.S. officials as she waited with her family.

“We risked our lives,” said the woman, who asked not to be named because of concerns for her family’s safety.