Eight leading technology companies on Monday called on the United States to overhaul its surveillance laws to better balance the needs of security and individual rights, in the wake of the NSA whistleblower Edward Snowden leaks.

In an open letter to US President Barack Obama and the US Congress, AOL, Apple, Facebook, Google, LinkedIn, Microsoft, Twitter and Yahoo said Washington should lead the way in a worldwide reform of state-sponsored spying.

"We understand that governments have a duty to protect their citizens. But this summer's revelations highlighted the urgent need to reform government surveillance practices worldwide," the letter said.

"The balance in many countries has tipped too far in favor of the state and away from the rights of the individual - rights that are enshrined in our Constitution.

"This undermines the freedoms we all cherish. It's time for a change."

They added: "We urge the US to take the lead and make reforms that ensure that government surveillance efforts are clearly restricted by law, proportionate to the risks, transparent and subject to independent oversight."

Since June, newspapers across the world have revealed the wide scope of government spying by publishing classified documents leaked by Snowden, a former US National Security Agency analyst now on the run in Russia.

Earlier, the NSA on Friday said its tracking of cellphones overseas is legally authorized under a sweeping US presidential order. The distinction means the extraordinary surveillance program is not overseen by a secretive US intelligence court but is regulated by some US lawmakers, Obama administration insiders and inspector-generals.

Documents obtained from Snowden showed that the NSA gathers as many as 5 billion records every day about the location data for hundreds of millions of cellphones worldwide by tapping into cables that carry international cellphone traffic. The Washington Post said the collection inadvertently scoops up an unknown amount of US data as well.

The NSA said on Friday it was not tracking every foreign phone call and said it takes measures to limit how much US data is collected. The NSA has declined to provide any estimates about the number of Americans whose cellphones it has tracked because they were traveling overseas or their data was irrevocably included in information about foreigners' cellphones.

"It is not ubiquitous," NSA spokeswoman Vanee Vines said. "NSA does not know and cannot track the location of every cellphone."

Vines said the collection of the global cellphone location data is carried out under the White House order that governs all US espionage, known as Executive Order 12333. That means congressional committees and relevant inspector-generals can oversee the program, but the secret court established under the Foreign Intelligence Surveillance Act would not.

AFP-AP