In his response to the senators on Tuesday, Alexander agreed that the fact sheet "could have more precisely described the requirements for collection."
“Given the intense interest from the media, the public, and Congress, we believe the precision of the source document (the statute) is the best possible representation of applicable authorities," Judith Emmel, an NSA spokeswoman, said in a separate statement explaining the move to take down the fact sheet.
In his letter, Alexander explained that Section 702 of the Foreign Intelligence Surveillance Act allows the NSA to collect information on people "reasonably believed to be outside of the United States."
Earlier this month, news reports revealed that the NSA has been using the 702 power to spy on the communications of Internet users through a program called PRISM.
Alexander said the NSA could not intentionally target a person inside of the United States or target a person outside of the United States if the purpose is to collect information on a person inside of the United States.
"NSA continues to support the effort led by the Office of the Director of National Intelligence and the Department of Justice to make publicly available as much information as possible about recently disclosed intelligence programs, consistent with the need to protect national security and sensitive sources and methods," Alexander wrote.