Citing documents obtained from former NSA contractor Edward Snowden and officials it characterized as knowledgeable, the Post said Wednesday the NSA, working with Britain's Government Communications Headquarters, secretly tapped into the Yahoo! and Google links, making it possible to collect data from hundreds of millions of user accounts, including the accounts of American users.
The newspaper said a top-secret document dated Jan. 9 showed an NSA department directs millions of records daily from Yahoo! and Google internal networks to data warehouses at its Fort Meade, Md., headquarters. The communications include text, audio and video as well as metadata identifying email senders and receivers.
The infiltration of Yahoo! and Google internal communications links is carried out using tools including a project named MUSCULAR -- operated by the NSA and GCHQ.
The White House and the Office of the Director of National Intelligence would neither confirm nor deny the report, the Post said.
Google issued a statement saying the company was "not aware of this activity" and was "troubled" by the report.
"We have long been concerned about the possibility of this kind of snooping, which is why we continue to extend encryption across more and more Google services and links," Goggle said.
"We have strict controls in place to protect the security of our data centers, and we have not given access to our data centers to the NSA or to any other government agency," a spokeswoman for Yahoo! said.
An EU delegation was to meet with White House officials in Washington Wednesday, following similar meetings with officials from the State Department, Congress and intelligence agencies, on U.S. spying on European leaders and citizens, CNN reported.
CNN said the talks were depicted as a chance to explore potential legal remedies for EU citizens affected by U.S. surveillance.
Leaders within the U.S. intelligence community have begun to push back against anger expressed by European leaders after allegations of surveillance based on information leaked by Snowden.
U.S. Army Gen. Keith Alexander, the NSA director, Tuesday denied allegations the United States collected telephone and email records from European citizens, calling reports "completely false."
Alexander and Director of National Intelligence James Clapper testified before the House Intelligence Committee, where lawmakers have called for a review of the intelligence-gathering process.
Clapper told lawmakers covert spying among nations was a "fundamental given," including attempts to access their communications. Clapper testified the NSA kept senior officials in the National Security Council informed of surveillance in foreign countries but didn't say specifically whether President Barack Obama was in the loop, The New York Times reported.
The White House has said it will re-examine the process by which such intelligence was collected.
Germany sent a separate delegation for a White House Wednesday discussion following reports Chancellor Angela Merkel's phone was tapped. Merkel said her country's confidence in the United States had been "shaken."
A senior administration official told the Times the overwhelming majority of intelligence it included in Obama's daily intelligence briefings focused on potential threats, such as al-Qaida plots or Iran's nuclear program.
"These are front-burner, first-tier issues," the official said. "He's not getting many briefings on intelligence about Germany."
Another administration official told the Times Obama generally doesn't rely on intelligence reports to prepare for meetings or phone calls with Merkel because they speak regularly and the two governments work together.
House Democrats and Republicans Tuesday introduced a bill that would curb some NSA practices, including bulk collection of telephone data within the United States. Sen. Dianne Feinstein, D-Calif., chairwoman of the Senate Intelligence Committee, vowed a "major review" of intelligence programs.