From NBC's Pete Williams
In an atmosphere of tension between the federal government and Arizona, the Justice Department today dialed it up some more, filing a lawsuit against Maricopa County Sheriff Joe Arpaio -- accusing him, the county, and his office with failing to cooperate with a civil rights investigation of his office.

The Justice Department has been investigating allegations that the sheriff's office has engaged in discrimination against Hispanics. As a recipient of federal funds, the sheriff's office is required to cooperate with such investigations.

But today, the Justice Department said it's been trying to get the sheriff's cooperation for more than a year without success. That makes his department "an extreme outlier," given that no other local law enforcement organization has refused to cooperate with a civil rights investigation in the last 30 years, the government says.

"The actions of the sheriff's office are unprecedented. It is unfortunate that the department was forced to resort to litigation to gain access to public documents and facilities," says Thomas Perez, the assistant attorney general for the Civil Rights Division.

*** UPDATE *** Arpaio responded to the lawsuit during a news conference in Phoenix, alleging that it amounted to harassment, the AP reports. "I think they know we have not been racial profiling, so what's the next step — camouflage the situation, go to the courts, and make it look like I'm not cooperating," he said.