Multiple planes are ready to take U.S. citizens and green card holders out of Afghanistan — but the Taliban won't let them leave, officials say

Multiple planes that are ready to take American citizens and green card holders out of the country are being denied permission to leave by the Taliban, congressional and NGO sources told CBS News.

Excerpts of an email from the State Department to members of congress viewed by CBS News acknowledged that charter flights are still on the ground at the Mazar-i-Sharif airstrip in northern Afghanistan and have permission to land in Doha "if and when the Taliban agrees to takeoff."  "The Taliban is basically holding them hostage to get more out of the Americans," a senior congressional source told CBS News.