REYKJAVIK, January 10, 2011 (AFP) - Iceland's foreign ministry said Monday it had summoned the United States' ambassador in Reykjavik over a US court call on Twitter to give details on WikiLeaks supporters, including an Icelandic MP.

"The foreign ministry summoned the American ambassador to a meeting this morning regarding a ruling by US authorities requesting website Twitter deliver personal documents on parliamentarian Birgitta Jonsdottir," the ministry said in a statement.

Jonsdottir was -- along with WikiLeaks head Julian Assange and two others -- named in a US court order and made public at the weekend for the micro-blogging website Twitter to supply private messages, contact information and IP addresses, among other details.

"There are reasonable grounds to believe that the records or other information sought are relevant and material to an ongoing criminal investigation," the order sent to Twitter read.

Iceland's foreign ministry said its permanent secretary and a legal adviser had "expressed serious concern that an Icelandic parliamentarian was subject to a criminal investigation" to US ambassador Luis Arreaga.

The officials emphasised that such an investigation could disrupt the parliamentarian's work, "including freedom of travel and the opportunities to participate in political debate on international level."

In Washington, State Department spokesman Philip Crowley said the ambassador had "a constructive discussion... and listened attentively to their concerns."

Arreaga, Crowley added, "took the opportunity to underscore how seriously the US takes the unauthorised disclosure of classified information and the harm it has caused.

"Our ambassador assured the government of Iceland that the Department of Justice investigation is being conducted in compliance with US law."

Jonsdottir, an early WikiLeaks supporter who distanced herself from the site a few months ago, is an active promoter of freedom of information and a member of the Icelandic parliament's foreign affairs committee.

She broke the news of the US court order to Twitter by writing about it at the weekend on her feed on the micro-blogging site.

"Just got this: Twitter has received legal process requesting information regarding your Twitter account in (relation to WikiLeaks)," she posted.

"I am speaking to US lawyers... because I want to try to stop that Twitter needs to hand over this information, on the principle," she told AFP Saturday.

On Monday, Jonsdottir tweeted she was travelling to Canada -- where she was set to speak about her Icelandic Modern Media Initiative -- via London instead of transiting in the United States.

"Heading for the airport - have to travel to Canada from Iceland via London instead of USA," she posted.

"The US government is trying to criminalize whistleblowing and publication of whistleblowing material, puts journalists at risk in the future," she added.