New York - A court overstepped its authority by trying to force the New York Police Department to release of hundreds of pages of documents about its infiltration of protest groups before the 2004 Republican National Convention, an appeals court found Wednesday.

The 2nd U.S. Circuit Court of Appeals in Manhattan reversed the district court's ruling that ordered the nation's largest police department to turn over secret "field reports" to protesters who sued the city over their arrests.

The ruling said that the city "met its burden of showing that law enforcement privilege applies to field reports - even as redacted by the district court - because the reports contain detailed information about the NYPD's undercover law enforcement techniques and procedures."

Before the convention, members of the NYPD's Intelligence Division went undercover and infiltrated protest groups that wanted to disrupt the convention. Information in the undisclosed documents "reinforces the city's assertions that the public faced a substantial threat of disruption and violence during the RNC," the appeals court wrote.

In a statement, city lawyer Celeste Koeleveld said the court agreed that the plaintiffs "have no compelling need for these sensitive materials."

More than 1,800 people were arrested at the four-day convention at Madison Square Garden, where President Bush accepted his party's nomination for a second term in office.