Washington - The National Security Agency has secretly broken into the main communications links that connect Yahoo and Google data centres around the world, the Washington Post reported on Wednesday, citing documents obtained from former NSA contractor Edward Snowden.A secret accounting dated 9 January 2013, indicates that NSA sends millions of records every day from Yahoo and Google internal networks to data warehouses at the agency's Fort Meade, Maryland, headquarters. In the last 30 days, field collectors had processed and sent back more than 180 million new records - ranging from "metadata," which would indicate who sent or received emails and when, to content such as text, audio and video, the Post reported on Wednesday on its website.The new details about the NSA's access to Yahoo and Google data centres around the world come at a time when Congress is reconsidering the government's collection practices and authority, and as European governments are responding angrily to revelations that the NSA collected data on millions of communications in their countries. Details about the government's programmes have been trickling out since Snowden shared documents with the Post and Guardian newspaper in June.The NSA's principal tool to exploit the Google and Yahoo data links is a project called Muscular, operated jointly with the agency's British counterpart, GCHQ. The Post said NSA and GCHQ are copying entire data flows across fibre-optic cables that carry information between the data centres of the Silicon Valley giants.Looser restrictionsThe NSA has a separate data-gathering program, called Prism, which uses a court order to compel Yahoo, Google and other Internet companies to provide certain data. It allows the NSA to reach into the companies' data streams and grab emails, video chats, pictures and more. US officials have said the programme is narrowly focused on foreign targets, and technology companies say they turn over information only if required by court order.In an interview with Bloomberg News on Wednesday, NSA Director General Keith Alexander was asked if the NSA has infiltrated Yahoo and Google databases, as detailed in the Post story."Not to my knowledge," said Alexander. "We are not authorised to go into a US company's servers and take data. We'd have to go through a court process for doing that."It was not clear, however, whether Alexander had any immediate knowledge of the latest disclosure in the Post report. Instead, he appeared to speak more about the Prism programme and its legal parameters.In a separate statement, NSA spokesperson Vanee Vines said NSA has "multiple authorities" to accomplish its mission, and she said "the assertion that we collect vast quantities of US persons' data from this type of collection is also not true."The GCHQ had no comment on the matter.The Post said the NSA was breaking into data centres worldwide. The NSA has far looser restrictions on what it can collect outside the United States on foreigners.But Google said the company has "long been concerned about the possibility of this kind of snooping." The statement said Google is "troubled by allegations of the government intercepting traffic between our data centres, and we are not aware of this activity".Google, which is known for its data security, noted that it has been trying to extend encryption across more and more Google services and links.Terrorism risksYahoo spokesperson Sarah Meron said there are strict controls in place to protect the security of the company's data centres. "We have not given access to our data centres to the NSA or to any other government agency," she said, adding that it is too early to speculate on whether legal action would be taken.The Muscular project documents state that this collection from Yahoo and Google has led to key intelligence leads, the Post said.Congress members and international leaders have become increasingly angry about the NSA's data collection, as more information about the programmes leak out.Alexander told lawmakers that the US did not collect European records, and instead the US was given data by Nato partners as part of a programme to protect military interests.More broadly, Alexander on Wednesday defended the overall NSA effort to monitor communications. And he said that as Congress considers proposals to scale back the data collection or provide more transparency to some of the programmes; it's his job to lay out the resulting terrorism risks."I'm concerned that we give information out that impacts our ability to stop terrorist attacks. That's what most of these programmes are aimed to do," Alexander said. "I believe if you look at this and you go back through everything, none of this shows that NSA is doing something illegal or that it's not been asked to do."Pointing to thousands of terror attacks around the world, he said the US has been spared much of that violence because of such programmes."It's because you have great people in the military and the intelligence community doing everything they can with law enforcement to protect this country," he said. "But they need tools to do it. If we take away the tools, we increase the risk."