US officials have issued a subpoena to demand details about WikiLeaks' Twitter account, the group announced today, adding that it suspected other American Internet companies were also being ordered to hand over information about its activities.

In a statement, WikiLeaks said U S investigators had gone to the San Francisco-based Twitter Inc to demand the private messages, contact information and other personal details of WikiLeaks founder Julian Assange and other supporters, including the U S Army intelligence analyst suspected of handing classified information to the site and a high-profile Icelandic parliamentarian.

WikiLeaks blasted the court order, saying it amounted to harassment.

"If the Iranian government was to attempt to coercively obtain this information from journalists and activists of foreign nations, human rights groups around the world would speak out," Assange said in the statement.

A copy of the court order, dated Dec 14 and posted to Salon.com, said the information sought was "relevant to an ongoing criminal investigation" and ordered Twitter not to disclose its existence to Assange or any of the others targeted.

The order was unsealed "thanks to legal action by Twitter," WikiLeaks said.

Twitter has declined comment on the claim, saying only that its policy is to notify its users, where possible, of government requests for information.

Others named in the order include Pfc. Bradley Manning, the U S Army private suspected of being the source of some of WikiLeaks' material, as well as Birgitta Jonsdottir, an Icelandic lawmaker and one-time WikiLeaks collaborator known for her role in pioneering Iceland's media initiative which aims to make the North Atlantic island nation a haven for free speech.

The US is also seeking details about Dutch hacker Rop Gonggrijp and US programmer Jacob Appelbaum, both of whom have previously worked with WikiLeaks.

Assange has promised to fight the order, as has Jonsdottir, who said in a Twitter message that she had "no intention to hand my information over willingly." Appelbaum, whose Twitter feed suggested he was travelling in Iceland, said he was apprehensive about returning to the US.

"Time to try to enjoy the last of my vacation, I suppose," he tweeted.

Gonggrijp expressed annoyance that court officials had misspelled his last name and praised Twitter for notifying him and others that the US had subpoenaed his details.