New documents reveal that the National Security Agency and the FBI are secretly gathering data from nine large U.S. internet companies.

The Washington Post reported that the secret wiretapping program codenamed PRISM may be unprecedented.

The internet companies involved include Microsoft, Yahoo, Google, Facebook, PalTalk, AOL, Skype, YouTube, and Apple, the report said.

The classified program allows the government agencies to extract audio, video, photographs, emails and documents to track individuals, according to the report.

Although some of the companies attempted to deny their cooperation with the widespread surveillance, they also avoided an outright denial about the program.

A report on Wednesday by Britain’s The Guardian revealed that Verizon, one of the largest telecommunications companies in the U.S., is required to hand over the telephone records of all its customers to the NSA on an “ongoing, daily basis.”

However, several security experts and a U.S. official said that it was likely that the practice extends to other phone carriers beyond Verizon.

The extensive surveillance practices began in 2007, during the George Bush administration, leaders of the Senate Intelligence Committee said on Thursday.

The Obama administration admitted to the classified program on Thursday while defending it as a necessary tool to ward off attacks.

Privacy advocates and civil liberties groups have blasted the surveillance as unconstitutional.

"This is a completely unwarranted violation of our constitutional rights," John Simpson, a consumer advocate at the group Consumer Watchdog, said via email.

"The United States should not be accumulating phone records on tens of millions of innocent Americans. That is not what democracy is about. That is not what freedom is about," said Senator Bernie Sanders, an independent from Vermont.