An encrypted email service believed to have been used by Edward Snowden, the American whistleblower, has shut down abruptly amid a legal fight that appeared to involve US government attempts to win access to customer information.
The US Department of Justice had no comment on Thursday's development.
"I have been forced to make a difficult decision: to become complicit in crimes against the American people, or walk away from nearly 10 years of hard work by shutting down Lavabit," Ladar Levison, Lavabit LLC owner, wrote in a letter that was posted on the Texas-based company's website.
This experience has taught me one very important lesson: without congressional action or a strong judicial precedent, I would strongly recommend against anyone trusting their private data to a company with physical ties to the United States.
He said he has decided to "suspend operations" but was barred from discussing the events over the past six weeks that led to his decision.
That matches the period since Snowden went public as the source of media reports detailing secret electronic spying operations by the US National Security Agency.
"This experience has taught me one very important lesson: without congressional action or a strong judicial precedent, I would strongly recommend against anyone trusting their private data to a company with physical ties to the United States," Levison wrote.
At a Moscow news conference four weeks ago, a Human Rights Watch representative said she had been contacted by Snowden from a Lavabit email address, according to news website GlobalPost.com.
Use of effective encryption by regular email users is rare.
Some of Snowden's leaked documents show that Google Inc, Microsoft Corp and other large providers have been compelled to help intelligence authorities gather email and other data on their users.
The big providers and other companies typically offer encryption but said they cooperate with legal requests, including those by intelligence officials.
Lavabit was an outlier, in part because it had said email was encrypted on its servers and could only be accessed with the user's password.
Snowden has been charged with espionage but was granted asylum by Russia, prompting US President Barack Obama to scrap a planned meeting with his Russian counterpart, Vladimir Putin.
Lavabit's statement suggested a gag order was in place, and lawyers said that could accompany any one of a wide range of demands for information.
The government could be seeking unencrypted versions of Snowden's email correspondence, other information about him, the technical means to decrypt his future emails or those of other customers, or basic information on all of Lavabit's hundreds of thousands of users.
It is rare and perhaps unprecedented for a legitimate US business to shut down rather than comply with a government request for information, said Kurt Opsahl, an attorney with the Electronic Freedom Foundation, a civil liberties group in San Francisco that is not involved in the case.
"This is a pretty extraordinary thing," Opsahl said. "I'm not aware of another case where a service provider elected to shut down under these kinds of circumstances."
Levison said the company has started preparing the paperwork needed to fight in the 4th Circuit Court of Appeals, which is based in Richmond, Virginia. He could not be reached for comment.
"All of this tells us the same lesson: almost nothing we do on the internet can be protected from government prying and spying," said Michael Ratner, a US lawyer who has worked for anti-secrecy website WikiLeaks, a Snowden ally.
"To talk privately, meetings will need to take place in large parks with plenty of tree cover."