Iceland called in the U.S. ambassador in Reykjavik on Monday to register its displeasure at a U.S. court's demand for details of an Icelandic lawmaker's Twitter account, the State Department said.

A U.S. court has ordered the social networking website to give up details of the accounts of WikiLeaks and of several supporters as part of a criminal investigation into WikiLeaks' release of hundreds of thousands of U.S. diplomatic cables.

The cables, disclosed by WikiLeaks to selected media groups as part of the website's campaign of exposing governments and corporations through the leak of previously private documents, have been a severe embarrassment to the U.S. government.

Our ambassador was called in. The government of Iceland expressed its concerns. I'll leave it to the government of Iceland to describe those concerns, State Department spokesman P.J. Crowley told reporters.

Ambassador Luis Arreaga had a constructive conversation ... and listened attentively to their concerns, he said. We took the opportunity to underscore how seriously the U.S. government takes the unauthorized disclosure of classified information and the harm it has caused.

A December 14 subpoena obtained by the U.S. Department of Justice and published by online magazine on Friday said the records sought from Twitter were relevant to an ongoing criminal investigation.

It ordered Twitter to provide account information on WikiLeaks founder Julian Assange and Bradley Manning, the U.S. Army intelligence analyst suspected of leaking Pentagon documents made public last year by WikiLeaks.

The information sought by the government includes all connection records and session times, IP addresses used to access Twitter, e-mail and residential addresses plus billing records and details of bank accounts and credit cards.

The subpoena included the accounts of WikiLeaks supporters Jacob Appelbaum, Rop Gonggrijp and Birgitta Jonsdottir, a former WikiLeaks volunteer and member of Iceland's parliament.

Over the weekend, WikiLeaks condemned the U.S. demand for the information, describing it as harassment.

Icelandic Foreign Minister Ossur Skarphedinsson told state radio on Saturday that the U.S. authorities' behavior was unacceptable and his government would do everything in its power to protect Jonsdottir.