HONG KONG (CNN) -- U.S. authorities are preparing charges against Edward Snowden, the man who outed himself as the source of secret documents detailing government surveillance of telephone and Internet communications, a law enforcement source told CNN on Tuesday.
The filing of charges is not imminent, however, the source said.
Snowden, 29, is a former computer security contractor who acknowledged in a Guardian newspaper interview published Sunday that he gave classified documents about the programs to journalists.
Lawmakers called for his prosecution as activists filed suits alleging the information gathering and surveillance has gone too far and violates the U.S. constitution
The FBI has been investigating the leaks, but it was unclear Tuesday how far along the agency was.
A federal law enforcement source told CNN on Monday that the investigation will include searches of Snowden's home and efforts to interview his girlfriend, relatives, co-workers and friends.
The official did not know if the FBI would attempt to contact Snowden overseas and ask if he would agree to a voluntary interview, or if the agency would wait until other evidence had been gathered.
Snowden himself told the Guardian that he expects to be charged under the Espionage Act and said he traveled to Hong Kong in hopes that state's commitment to free speech would prevent his extradition to the United States.
Snowden has disappeared since giving those interviews in a Hong Kong hotel room. Ewen MacAskill, one of the Guardian journalists who worked with him, said Tuesday that Snowden was still in Hong Kong.
Snowden's disclosures have fueled new debate about the U.S. government's collection of records of domestic telephone calls and overseas Internet activity in the global hunt for terrorists and criminals.
Civil liberties advocates say the measures are an unacceptable intrusion into citizens' privacy. But supporters of the programs say they are legal and have yielded evidence that has helped put terror plotters in prison, though many of the details remain classified.
Obama administration officials and leaders of the intelligence committees in Congress say the program undergoes periodic review by all three branches of government, and that the content of Americans' calls is not being monitored.
White House spokesman Jay Carney said Monday that the measures are a necessary middle way between total privacy and unacceptable threat.
Some European lawmakers, however, said Tuesday in a European Parliament debate in Brussels, Belgium, that the Internet surveillance program does not appear to meet European data standards, according to an account published to the European Union website.
"My data belongs to me, that is the cornerstone of European thinking on data protection," said Manfred Weber, a member of the European Parliament from Germany.
He called the differing U.S. rules for American and overseas data "completely unacceptable."
Other lawmakers called for sanctions against the U.S.-based companies that have provided customer information to the National Security Agency surveillance program.
But not all of the legislators were ready to condemn the United States.
"Those companies already named and shamed have so far denied acting outside the law," said British member of parliament Timothy Kirkhope. "Yet here we are already pointing the finger, some of you already expressing anti-American or anti-commission rhetoric."
The European Commission plans to discuss the issue with U.S. officials at a meeting Friday in Dublin, Ireland, Commissioner Tonio Borg said.
"Programs such as the so-called PRISM and the laws on the basis of which such programs are authorized potentially endanger the fundamental right to privacy and to data protection of EU citizens," he said.
Uncertainty over next move
Snowden last worked for the computer consulting firm Booz Allen Hamilton.
The company fired him Monday after less than three months on the job for violations of company policy and its code of ethics. Despite what he had said was a $200,000 salary, the company said he earned $122,000.
It's unclear what's next for him.
Although Hong Kong is part of communist-ruled China, the former British colony has a separate system of government that allows a free press and tolerates political dissent.
But legal experts say Hong Kong's extradition treaty with the United States could make it hard for Snowden to successfully fight any proceedings against him unless he is able to prove, for example, that any charges against him are politically motivated.
Patricia Ho, a lawyer with Daly & Associates in Hong Kong, whose firm has handled asylum and refugee claims, said that given Hong Kong's lackluster track record on granting asylum, she was surprised that Snowden had lauded the territory for its commitment to civil liberties.
"Within China itself, Hong Kong has better civil liberties, but I couldn't see the Hong Kong government granting him asylum given their present practices," she said.
On Monday, the office of Russian President Vladimir Putin's spokesman tweeted that U.S. officials had broken the law with the surveillance programs, making Snowden a "human rights activist."
Spokesman Dmitry Peskov told CNN that Russia would consider an asylum request from Snowden, but has not received one.
Advice from Assange
Snowden has told the Guardian that he hopes to seek asylum, potentially in Iceland because of the way it dealt with WikiLeaks, a group that facilitates the anonymous leaking of secret information through its website. The group reportedly once operated from there.
WikiLeaks founder Julian Assange, bottled up in the Ecuadorian Embassy in London since last June, said Snowden should be looking to the southeast, not northwest.
"I would strongly advise him to go to Latin America," Assange told CNN's "Anderson Cooper 360" on Monday night. "Latin America has shown in the past 10 years that it is really pushing forward in human rights. There's a long tradition of asylum."
Assange sought refuge in the Ecuadorian mission to avoid extradition to Sweden, where he is wanted for questioning over allegations that he raped one woman and sexually molested another. He has repeatedly said the allegations in Sweden are politically motivated and tied to the work of his website.
Assange has said he fears Sweden will transfer him to the United States.
Traveling to another country could become difficult for Snowden if U.S. authorities issue an Interpol "red notice" against him, according to Don Borelli, a former FBI agent and U.S. legal attache overseas.
"Many countries recognize an Interpol red notice as kind of a universal arrest warrant," he said.
More revelations coming
Glenn Greenwald, one of the Guardian journalists who broke the NSA story, says the newspaper is not finished revealing NSA secrets.
"There are extremely invasive spying programs that the public still does not know about that the NSA regularly engages in or other capabilities that they're developing," he said in an interview with CNN's Christiane Amanpour on Monday.
"We are working on stories right at this moment that we think are very valuable for the public to know that don't in any way harm national security but that shine a light on this extremely secretive though momentous agency," he said.
Jethro Mullen reported and wrote from Hong Kong; Michael Pearson reported and wrote from Atlanta; CNN's Matt Smith, Joe Johns, Carol Cratty, Tom Cohen, Brian Walker, Elise Labott and Alla Eshchenko contributed to this report.