WASHINGTON - In another case of the Obama administration's investigating classified information improperly disclosed to reporters, the government is prosecuting a State Department expert on North Korea in a probe that appears to step into uncharted territory - by declaring that a journalist is committing a crime in disclosing leaked information.

During the investigation of State Department adviser Stephen Kim, law enforcement officials obtained a search warrant for some private e-mails of James Rosen, the chief Washington correspondent for Fox News. Investigators also tracked Rosen's comings and goings from the State Department.

An FBI agent seeking the search warrant spelled out the government's view of the journalist's role, saying that the reporter was a coconspirator and that there was probable cause to believe that the reporter committed a violation of criminal law.

"We are outraged to learn today that James Rosen was named a criminal coconspirator for simply doing his job as a reporter," said Michael Clemente, Fox's executive vice president for news. "In fact, it is downright chilling. We will unequivocally defend his right to operate as a member of what up until now has always been a free press."

Kim, who is awaiting trial, is accused of revealing secrets to the news organization. No charges have been filed against Rosen.

The Kim case is further along than a more recent leak probe in which prosecutors secretly subpoenaed Associated Press phone records. In the AP case, AP President and Chief Executive Gary Pruitt said the government's conduct has already had a chilling effect on newsgathering, a week after the AP subpoenas were revealed publicly.

In June 2009, Rosen reported that U.S. intelligence officials warned President Obama and senior U.S. officials that North Korea would respond to a U.N. Security Council resolution condemning nuclear tests with another nuclear test.

The 2010 affidavit for a search warrant, first reported by the Washington Post, does not identify Rosen as "the reporter," but he wrote the story at issue, and Fox News confirmed Monday that it was him.

The White House wouldn't comment about tracking Rosen, citing an ongoing criminal investigation.