The Obama administration has asked a federal judge to throw out a lawsuit against Iran filed by Americans held hostage at the U.S. Embassy in Tehran 30 years ago.

The request comes in a $6.6 billion class-action lawsuit filed in U.S. District Court in Washington. Fifty-two American diplomats and military officials were held captive for more than a year at the end of Jimmy Carter's presidency by a group of Islamist students who supported the Iranian revolution.

The hostages were released on Jan. 20, 1981, just minutes after Ronald Reagan was sworn in as the new president.

In court papers filed Tuesday night without any announcement, the Justice Department argued that the agreement to release the hostages, known as the Algiers Accords, precluded lawsuits against Iran.

A similar lawsuit brought by the Iranian hostages was dismissed in 2000 after the government successfully argued it was banned by the Algiers Accords. The hostages argue that legislation passed by Congress last year and signed into law by President George W. Bush gives them the right to bring private lawsuits.

But the Justice Department argued that the law does not mention the Algiers Accords, much less explicitly repeal them.

"The gratitude of the United States for the service and dedication of these brave individuals cannot be overstated, nor can the suffering and abuse they endured on behalf of this country be exaggerated; these matters are beyond dispute," the Justice Department wrote in its filing.

The hostages argue that Iran supported their confinement and abuse, with visits from government officials, stays in government prisons and buildings and threats of trial in Iranian courts. The lawsuit says current Iranian President Mahmoud Ahmadinejad was one of their interrogators.

The lawsuit says the hostages were tortured, beaten sometimes until they lost consciousness and kept in fear of their lives, at times even lined up in front of marksmen locking their guns. It says they were imprisoned without adequate food, clothing or medical care, blindfolded with their hands tied, interrogated for hours at a time and kept in isolation for months at a time.

The original plaintiffs are three of the hostages -- Charles Scott of Jonesboro, Ga., David Roeder of Alexandria, Va., and Don Sharer of Mansfield, Texas -- and the wife and daughter of another hostage, Barry Rosen, from New York City.