US authorities have obtained a secret court order to force search giant Google and a small Internet provider to hand over information from email accounts of a volunteer for whistleblower website WikiLeaks, a report said.

The Wall Street Journal, citing documents it had reviewed, said the Internet service provider Sonic had been forced to turn over the data from the email of Wikileaks volunteer Jacob Appelbaum.

Sonic said it resisted the order but lost the legal battle, and had to pass on the information on email addresses Appelbaum had corresponded with over the past two years, according to the Journal.

Appelbaum, 28, has not been charged with any criminal conduct, while the financial daily said Google and Sonic had both called for him to be informed of the secret court order that targeted him.

WikiLeaks has angered US authorities for posting secret documents on the wars in Afghanistan and Iraq and releasing a slew of internal correspondence among US diplomats around the world.

The revelation of a secret court order raises questions around US authorities' ability to obtain information on people's digital correspondence -- by email and cellphone -- and whether the law, the Electronic Communications Privacy Act, violates constitutional protections over search and seizure.