(CNN) – Leaks disclosing important national security information should be investigated by a special prosecutor, independent Sen. Joe Lieberman said Sunday.
"I've been thinking about this since these leaks came out and I've reached a conclusion which is that we do need a special counsel," Lieberman said on "Fox News Sunday."
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A report in The New York Times earlier this month that provided classified details of what it described as a U.S. cyberattack targeting Iran's nuclear centrifuge program sparked bipartisan outrage. Other recent possible leaks of classified information included details on the administration's efforts to expand its drone program and President Barack Obama's involvement in "kill lists" against militants in Yemen and Pakistan.
U.S. Attorney General Eric Holder assigned two U.S. attorneys to lead investigations into the possible leaking of state secrets, but Lieberman said Sunday the fact that one of the attorneys had made donations to Obama's presidential campaign meant he couldn't reach an unbiased decision.
"No matter what he concludes, people are going to say it was biased," Lieberman, who caucuses with Democrats in the U.S. Senate, said on Sunday.
"We need a special counsel because a special counsel avoids any appearance of conflict of interest," he continued. "Special counsels, independent counsels before them were created for a situation exactly like this where people might reach a conclusion that investigators. U.S. attorneys even, working for the attorney general appointed by the president, cannot independently and without bias investigate high officials of their own government."
With his call for an independent special counsel, Lieberman joins Republicans who have also called into question Holder's decision to investigate using U.S. attorneys. Last Sunday, Sen. John McCain, R-Arizona, said on CNN that the attorney general had lost all credibility with Congress.
"This needs a special counsel, someone entirely independent of the Justice Department," McCain said.
David Plouffe, a senior White House adviser to Obama, said again Sunday the Justice Department investigation using U.S. attorneys would adequately probe the leaks.
There are going to be two U.S. attorneys "who have been appointed by the attorney general, including a Bush appointee," Plouffe said. "We are going to look at this thoroughly as it should."