A friend of Bradley Manning, the American soldier accused of leaking classified files to WikiLeaks, said he declined to answer questions Wednesday at a grand jury hearing.

Prosecutors, who have not given up bringing charges against the whistle-blower website's founder Julian Assange, had subpoenaed David House to testify before the grand jury in Alexandria, Virginia.

But House said that during the closed-door hearing he invoked the constitution's Fifth Amendment, which protects him from self-incrimination, offering only his name and address and refusing to answer the prosecutors other questions.

"The show trial that is now under way in Alexandria, Virginia has the potential to set a dangerous precedent for regulating the media," House said in a statement issued by Manning's support network.

"Using Nixonian fear tactics that were honed during the Pentagon Papers investigation, the DoJ (Department of Justice) is attempting to dismantle a major media organization -- WikiLeaks -- and indict its editor, Julian Assange," he said.

"The DoJ's ever-widening net has now come to encompass academics, students, and journalists in the Cambridge (Boston) area," he said.

President Barack Obama's administration is seeking to force these individuals to testify "against this media organization in an attempt to cast its publications and those of its media partners -- the New York Times, the Guardian, Der Spiegel, Le Monde, and El Pais -- as acts of espionage."

Grand juries, which are empanelled to determine whether there is sufficient evidence to bring charges in a case, typically meet in secret unless a witness discloses that he or she has been summoned to testify.

Although the hearing does not mean that charges against Assange are imminent, it is a strong indication that the US administration, as promised, continues to pursue that goal.

It opened a criminal investigation against Assange in July 2010, following a massive document dump by his website that continues to roil US relations with countries around the world.

One possible avenue open to prosecutors is to show that Assange personally asked Manning, a US army private, to obtain confidential documents.

Manning is awaiting a possible court martial on charges that include "aiding the enemy," which carries a maximum penalty of life in prison.

Assange, 39, is under house arrest in Britain, awaiting trial on sexual assault and molestation charges in Sweden.

He has denied knowing the source of the leaks, but has defended Manning as a victim of US government mistreatment.