The Obama administration has launched an internal review of the potential damage to national security from leaks about US surveillance efforts, as a group of senators and technology companies push the government to be more open about the top-secret programmes.
A senior US intelligence official said on Tuesday that the review will be separate from a criminal investigation by the Justice Department into Edward Snowden's disclosures about the broad monitoring by the National Security Agency (NSA) of phone call and internet data from big companies such as Google Inc and Facebook.
The exercise is expected to address whether the leaks have compromised sources or surveillance methods, and would probably look for chatter among intelligence targets to see if they have changed tactics due to the leaks.
Big technology companies, for their part, issued a series of pleas on Tuesday for the government to lift the veil on national security requests to the private sector.
Jay Carney, the White House spokesman, fended off all questions on Tuesday about Snowden, 29, who was last known to be in Hong Kong, on the grounds that a legal investigation was under way.
Reporters staked out hotels in Hong Kong in hopes of spotting Snowden, an NSA contractor who went public in a video released on Sunday by Britain's Guardian newspaper but then dropped from sight in the former British colony and has yet to resurface.
Felony charges considered
As part of its criminal investigation, US Justice Department is considering felony charges against Snowden while the FBI is speaking with Snowden’s friends and relatives and gathering evidence to build the US government’s case.
The White House says the NSA intelligence programmes are legal and are subject to adequate oversight by Congress and the judiciary.
The Republican Speaker of the House of Representatives, John Boehner, earlier described Snowden's actions in leaking details of NSA programmes to the Guardian and Washington Post newspapers as a "giant" violation of law.
"He's a traitor," Boehner told ABC News in an interview.
"The disclosure of this information puts Americans at risk. It shows our adversaries what our capabilities are."
Dianne Feinstein - the Democratic chairperson of the Senate Permanent Select Committee on Intelligence - has said US authorities are vigorously pursuing Snowden.
Booz Allen Hamilton, the company that most recently employed Snowden, said it had terminated Snowden's employment on Monday for violations of its code of ethics and policies.
It said he had been an employee for less than three months at an annual salary rate of $122,000.
Members of Congress promised an extensive public discussion and more legislative efforts to tighten the laws on US government surveillance.
"We'll have a lot of hearings on this," Senator Barbara Mikulski, a Democrat, said. She said there were questions about how Snowden, a high-school dropout, gained a top-secret clearance and access to high-level government secrets.
A bipartisan group of senators introduced a bill designed to end the secret supervision of the programmes by the Foreign Intelligence Surveillance Court by requiring declassification of significant court rulings.
"Americans deserve to know how much information about their private communications the government believes it's allowed to take under the law," Senator Jeff Merkley, a Democrat, said.
Civil liberties case
In another development, American Civil Liberties Union (ACLU), the best known civil rights group in the US, lodged a lawsuit on Tuesday alleging that the seizure of private phone records by government agents breached the constitution.
The details leaked leaked by Snowden include an operation to seize phone data from operator Verizon.
The scheme collected "metadata" - the timing, location and destination but not the content - of calls made by millions of Americans, angering groups such as ACLU.
"This dragnet programme is surely one of the largest surveillance efforts ever launched by a democratic government against its own citizens," Jameel Jaffer, ACLU deputy legal director, said in a statement announcing the lawsuit.
"It is the equivalent of requiring every American to file a daily report with the government of every location they visited, every person they talked to on the phone, the time of each call, and the length of every conversation.
"The programme goes far beyond even the permissive limits set by the Patriot Act and represents a gross infringement of the freedom of association and the right to privacy," Jaffer said, referring to a law passed after the 9/11 attacks.
The group said it had filed suit with the FISA court, a secret chamber set up under the Foreign Intelligence Surveillance ACT to oversee government spying, alleging that the Verizon order breached the US constitution.
The ACLU, like millions of US individuals and entities, is a Verizon customer, allowing it to make a direct complaint on its own behalf.
Little public outcry
In addition to the phone sweep, Snowden revealed a global programme by US intelligence agencies to monitor the Internet data of foreigners abroad.
But aside from a handful of legislators calling for the surveillance programmes to be curtailed, there has been little public and Congressional outcry yet, Al Jazeera's Kimberly Halkett reported from Washington DC.
"It seems most Americans - for now at least - are giving the government the benefit of the doubt," she said.
Nearly half of all Americans say the US government's broad surveillance tactics are acceptable within limits, according to a Reuters/Ipsos poll on Tuesday that also found widespread concern about the methods that were revealed last week.
The poll, conducted from Friday to Tuesday, found that few were completely untroubled by the news that the NSA has been secretly monitoring telephone and Internet activity of millions of Americans.