A supporter of the Army private suspected of supplying classified documents to the WikiLeaks website on Wednesday refused to testify to a federal grand jury, accusing the U.S. justice department of using Nixon-like fear tactics to intimidate advocates of transparency in government.

David House, a founding member of the Bradley Manning Support Network, said he invoked his Fifth Amendment rights against self-incrimination after being subpoenaed to the federal courthouse in Alexandria. Prosecutors have convened a grand jury there to investigate the WikiLeaks disclosures.

House told reporters after his appearance that nearly all the questions posed by prosecutors centered on Bradley Manning, who is being held at Fort Leavenworth while military authorities conduct their own investigation into whether he illegally leaked sensitive documents about the Iraq and Afghanistan wars. House said he was not asked any questions about WikiLeaks founder Julian Assange.

The Justice Department, House said, "is very frantically trying to link Bradley Manning and Julian Assange, and they're casting a very wide net."

His lawyer Peter Krupp said that while House has done nothing wrong, he invoked his right against self-incrimination because "any testimony he would give would be manipulated to be used against him." Krupp also accused prosecutors of using the grand jury to trample on House's right to freely associate with Manning or other WikiLeaks supporters.

Prosecutors, if they choose, could give House immunity for his testimony and compel him to answer questions. If House still refused to testify, he could then be charged with contempt of court and sent to jail to try and force his testimony.

Krupp said prosecutors gave no indication whether they would grant House immunity, and no decision has been made on what House will do if he gets immunity.

U.S. Attorney Neil MacBride spokesman Peter Carr declined comment.

About 20 supporters of House and Manning staged a rally outside the courthouse to offer support. Ray McGovern, a former CIA analyst, said that while it's important for soldiers and civilians to honor their promises to keep classified information secret, it's more important to expose wrongdoing within the government that is going unchecked.

"I'm talking about stopping war crimes. ... I'm talking about bringing people to justice. Bradley Manning, at the tender age of 22, was able to see this," McGovern said. "I have every reason to believe that was his motivation."

House, 24, a freelance computer scientist from Boston, said he, too, understands the government's desire to protect information that's vital to national security. But he said the documents exposed by WikiLeaks provide a vital watchdog role exposing government wrongdoing, including military attacks on civilians and foreign policy missteps.

"WikiLeaks has been cast as a breach of national security because the U.S. government has been embarrassed by the disclosures," House said. "I don't want to wake up every morning and just read how glorious the U.S. government is."