An encrypted email service believed to have been used by US leaker Edward Snowden shut down on Thursday apparently as a result of pressure from US authorities.

Lavabit owner Ladar Levison posted a message at the website telling users that the he was pulling the plug on the secure email service launched in Texas nearly a decade ago.

"I have been forced to make a difficult decision: to become complicit in crimes against the American people or walk away from nearly ten years of hard work by shutting down Lavabit," Levison said.

"After significant soul searching, I have decided to suspend operations."

Levison lamented that he was barred from sharing details of what prompted Lavabit's demise.

US law allows national security officials to make requests to companies that come with the caveat they must be kept secret.

"As things currently stand, I cannot share my experiences over the last six weeks, even though I have twice made the appropriate requests," Levison said.

Lavabit was put in the spotlight after it was reported that former US National Security Agency contractor Snowden was using the service to exchange messages while he was holed-up in the Moscow airport.

Snowden is a fugitive from US justice and is currently living at an unknown location in Russia after Moscow granted him temporary asylum for a year on August 1.