Larry Page and Mark Zuckerberg sharply deny knowledge of Prism until Thursday even as Obama confirms program's existence

America's tech giants continued to deny any knowledge of a giant government surveillance programme called Prism, even as president Barack Obama confirmed the scheme's existence Friday.

With their credibility about privacy issues in sharp focus, all the technology companies said to be involved in the program issued remarkably similar statements.

All said they did not allow the government "direct access" to their systems, all said they had never heard of the Prism program, and all called for greater transparency.

In a blogpost titled 'What the…?' Google co-founder Larry Page and chief legal officer David Drummond said the "level of secrecy" around US surveillance procedures was undermining "freedoms we all cherish."

"First, we have not joined any program that would give the US government – or any other government – direct access to our servers. Indeed, the US government does not have direct access or a 'back door' to the information stored in our data centers. We had not heard of a program called Prism until yesterday," they wrote.

"Second, we provide user data to governments only in accordance with the law. Our legal team reviews each and every request, and frequently pushes back when requests are overly broad or don't follow the correct process."

The Google executives said they were also "very surprised" to learn of the government order made to obtain data from Verizon, first disclosed by the Guardian. "Any suggestion that Google is disclosing information about our users' internet activity on such a scale is completely false," they wrote.

Mark Zuckerberg, the founder and CEO of Facebook, described the press reports about Prism as "outrageous". He insisted that the Facebook was not part of any program to give the US government direct access to its servers.

He said: "Facebook is not and has never been part of any program to give the US or any other government direct access to our servers. We have never received a blanket request or court order from any government agency asking for information or metadata in bulk, like the one Verizon reportedly received. And if we did, we would fight it aggressively. We hadn't even heard of Prism before yesterday."

Zuckerberg also called for greater transparency. "We strongly encourage all governments to be much more transparent about all programs aimed at keeping the public safe. It's the only way to protect everyone's civil liberties and create the safe and free society we all want over the long term."

Yahoo said: "We do not provide the government with direct access to our servers, systems, or network."

The leaked National Security Agency (NSA) document obtained by the Guardian claims Prism operates with the "assistance of communications providers in the US".

The document names AOL, Apple, Facebook, Google, Microsoft, PalTalk and Yahoo and gives dates when they "joined" the scheme, aimed at intercepting data from people outside the US.'' The presentation talks of "legally compelled collection" of data.

All the companies involved have now denied knowledge of the scheme to the Guardian.

In one slide, the presentation identifies two types of data collection: Upstream and Prism. Upstream involves the collection of communications on "fibre cables and infrastructure as data flows past." Prism involves: "Collection directly from the servers of these US service providers: Microsoft, Yahoo, Google, Facebook, PalTalk, AOL, Skype, YouTube, Apple."

Obama confirmed the existence of the scheme Friday and said Congress was "fully apprised" of the situation and that it was being conducted legally with a "whole range of safeguards involved".

But despite Obama's acknowledgment, senior figures said they remained puzzled and surprised by the news. Speaking off the record one said their company regularly complied with subpoenas for information but had never allowed "collection directly" from their servers.

Some speculated that the wording of the document was incorrect or that the author had over-hyped the scheme.

Security experts and civil liberty figures were less convinced. "I was assuming that these tech companies were just lying," said security guru Bruce Schneier. "That's the most obvious explanation."

"Could it possibly be that there's a department within these companies that hides this from the executives? Maybe," he said. "I don't know, we don't know. This points to the problem here. There's so much freaking secrecy that we don't know enough to even know what is going on."

He said he was not surprised by the news. "There are no surprises here. We all knew what was going on and now they have finally admitted it."

"The NSA would not have done this surreptitiously, they want the tech companies on their side," said Jameel Jaffer, director of the American Civil Liberties Union (ACLU). "I can't make sense of their statements at all."

He said it was clear that tech companies in general were more than happy to co-operate with the US authorities and said he was puzzled why there seemed to be such a gap between the two sides' story.

Ali Reza Manouchehri, CEO and co-founder of MetroStar Systems, an IT consultant that works closely with government agencies, said: "There are situations that come up where they have to communicate with the security agencies. At the end of the day they are working in the interest of national security."

"I can't comment on what's going on inside the company. It's hard for me to believe that Google doesn't know," he said. "It is either transparent or it is surreptitious. It is hard for me to believe that at this level, at this volume it is surreptitious." He said if the companies really did not know then "we have some serious issues."

The news has sparked widespread concern in the US. Nearly 20,000 people have signed a petition at Progressive Change Campaign Committee calling on Congress to hold investigations.