At least four planes chartered to evacuate several hundred people seeking to escape the Taliban‘s takeover of Afghanistan have been unable to leave the country for days, officials said Sunday. Reports on why they are stuck are conflicting as pressure ramps up on the United States to help those left behind to flee.

One theory is that the would-be passengers were Afghans, many of whom did not have passports or visas, and thus were unable to leave the country. An Afghan official at the airport in the northern city of Mazar-e-Sharif said that they had left the airport while the situation was sorted out, the Associated Press reported.

But according to the top Republican on the US House Foreign Affairs Committee, the group included Americans and they were sitting on the planes, but the Taliban were not letting them take off, effectively “holding them hostage.” He did not, however, say where that information came from.

“The Taliban will not let them leave the airport. I am worried they are going to demand more and more, whether it be cash or legitimacy as the government of Afghanistan,”  Representative Michael McCaul of Texas told “Fox News Sunday” He did not offer more details.

The accounts could not be immediately reconciled.

The final days of America’s 20-year war in Afghanistan were marked by a harrowing airlift at Kabul‘s airport to evacuate tens of thousands of people — Americans and their allies — who feared what the future would hold, given the Taliban’s history of repression, particularly of women. When the last troops pulled out on August 30, though, many were left behind.

The US promised to continue working with the new Taliban rulers to get those who want to leave out, and the militants pledged to allow anyone with the proper legal documents to leave. The reports are bound to put more pressure on the government.

The Afghan official, who spoke on condition of anonymity because of the sensitivity of the subject, said it was four planes, and their intended passengers were staying at hotels while authorities worked out whether they might be able to leave the country. The sticking point, he indicated, is that many did not have the right travel papers.

According to the AP reports, residents of Mazar-e-Sharif also said the passengers were no longer at the airport. At least 10 families were seen at a local hotel waiting, they said, for a decision on their fates. None of them had passports or visas but said they had worked for companies allied with the US or German military. Others were seen at restaurants.

(With AP inputs)