ALEXANDRIA, Virginia – Lawyers for three Twitter users Tuesday asked a US federal judge to overturn a court order directing the microblogging site to hand over clients' data to the US government for use in a probe into WikiLeaks.

The order calling on Twitter to release data about the accounts of Birgitta Jonsdottir, an Icelandic lawmaker, US computer researcher Jacob Appelbaum, and Rop Gonggrijp, a Dutch volunteer for WikiLeaks, was handed down in December by Judge Theresa Buchanan, the same judge who heard Tuesday's challenge.

Buchanan on December 14 ordered Twitter to hand over to the US government information on the three subscribers, who were represented but did not appear in court Tuesday, and any other clients linked to WikiLeaks, the organization led by Julian Assange that last year released a slew of diplomatic cables.

The information that Buchanan said should be handed over by Twitter included Internet Protocol addresses and the addresses of "tweet" recipients.

But complying with the order would allow the US government to "map the associations" of Twitter users, and know when, from where and to whom they are sending messages, said John Keker, representing Appelbaum.

That was a breach of privacy, which is guaranteed by the fourth amendment of the US constitution, he said.

John Davis argued for the government that asking for the data was "a standard investigative measure that is used in criminal investigations every day of the year all over the country."

The hearing was held as US Secretary of State Hillary Clinton gave a speech on Internet freedom at George Washington University in Washington, saying the United States is "committed to continuing our conversation with people around the world."

"The demand for access to platforms of expression cannot be satisfied when using them lands you in prison," Clinton said in the speech, referring to crackdowns on bloggers and Twitter users in countries like Syria or Iran.

In the Virginia courtroom, meanwhile, lawyers for the three Twitter users also asked Buchanan to unseal, or make public, still secret documents related to the December order.

The documents are widely believed to contain information about other companies -- including Google, Facebook and Yahoo -- from which the US government has tried to collect client data for its WikiLeaks probe.

"The government shouldn't be able to get this information in the first place, and shouldn't be able to get it in secret," American Civil Liberties Union (ACLU) senior attorney Aden Fine, one of the lawyers representing Jonsdottir, said in his arguments to Buchanan.

Giving the US authorities access to information of social networking sites' clients was "something brand new which, if allowed, would permit the government to know a lot more about us electronically than it used to," said Keker.

In Jonsdottir's case, the US government's and court's actions are "especially troubling" because they show a disregard for Icelandic law, which gives lawmakers in the Nordic country broad immunity, Cindy Cohn of the Electronic Frontier Foundation (EFF) told AFP.

"Courts usually try to honor another country's laws," she said, echoing something Fine had said during the hearing, which lasted slightly more than an hour.

"The entire world is watching to see what the US government's and the courts' response will be to this," he said.

Judge Buchanan said she would mull both sides' arguments and announce her decision, but did not say when that would be.