WASHINGTON  Prosecutors investigating the disclosure of thousands of classified government documents by the anti-secrecy group WikiLeaks have gone to court to demand the Twitter account activity of several people linked to the organization, including its founder, Julian Assange, according to the group and a copy of a subpoena made public late Friday.

The subpoena is the first public evidence of a criminal investigation, announced last month by Attorney General Eric H. Holder Jr., that has been urged on by members of Congress of both parties but is fraught with legal and political difficulties for the Obama administration. It was denounced by WikiLeaks, which has so far made public only about 1 percent of the quarter-million confidential diplomatic cables in its possession but has threatened to post them all on the Web if criminal charges are brought.

Dozens of Pentagon and State Department officials have worked for months to assess the damage done to American diplomatic and military operations by the disclosures. In recent weeks, Justice Department officials have been seeking a legal rationale for charging Mr. Assange with criminal behavior, including whether he had solicited leaks.

The move to get the information from five prominent figures tied to the group was revealed late Friday, when Birgitta Jonsdottir, a former WikiLeaks activist who is also a member of Iceland’s Parliament, received an e-mail notification from Twitter.