A U.S. document containing sensitive details about hundreds of civilian nuclear sites across the country was posted online Monday, an apparently inadvertent security breach that had federal officials scrambling yesterday to remedy the mistake.

The document, a draft declaration of U.S. nuclear facilities to the U.N. nuclear watchdog agency, contained descriptions of sensitive civilian sites, including the locations of facilities that store enriched uranium and other materials used in nuclear weapons. It was available for about a day on a Government Printing Office Web site before inquiries by news organizations prompted its hasty removal.