A second United States email service has shut down amid reports that the US government was attempting to gain access to encrypted messages sent by whistleblower Edward Snowden.
A company named Silent Circle on Friday said it would close its secure email service, hours after Lavabit said it would shut down rather than "become complicit in crimes against the American people".
"We see the writing on the wall, and we have decided that it is best for us to shut down Silent Mail," the statement said on Friday, citing the Lavabit decision.
"We have not received subpoenas, warrants, security letters, or anything else by any government, and this is why we are acting now."
Snowden is reported to have used the Lavabit service to communicate with journalists and share information about the National Security Agency's huge spying programme targeting American citizens and millions of foreigners.
The owner of Lavabit, Ladar Levison, said in a statement on Thursday: "I have been forced to make a difficult decision. As things currently stand, I cannot share my experiences over the last six weeks, even though I have twice made the appropriate requests."
No privacy guarantee
Those six weeks match the period since Snowden leaked information about huge secret electronic spying operations by the US National Security Agency, suggesting the government was trying to access Lavabit's servers and had gagged the company from saying so.
"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.
Unlike popular email services such as Google Mail, Lavabit allowed users to securely encrypt messages on its servers, which could then only be accessed with the user's password.
Lavabit's statement did not name Snowden or refer to any particular investigation, but the statement's timing - and other material in the public domain - suggest that it was being compelled by the NSA to give them access to Snowden's account, and decided to shut down rather than comply.
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.