On a normal day the stone halls of the National Library of Spain echo with the steps of academics researching obscure topics. This week, however, they have been joined by police on the trail of international art thieves.

The head of the library, the writer Rosa Regàs, quit her post this week after it emerged that two valuable world maps from its rare 1482 editions of Ptolemy’s Cosmographia had disappeared from the Cervantes Hall. Police who searched the hall, which is restricted to professional researchers, found pages torn from four other books, dating from the 16th and 17th centuries.

The stolen maps are “incredibly important ... the cream of many collections”, Daniel Crouch, a leading map dealer from the Shapero Gallery in London, told The Times.

“It is the most important map from a cornerstone atlas, the second-most-desirable of the 15th century.” Despite the embarrassing loss of two maps valued at $100,000 (£50,000) apiece, Ms Regàs has not gone quietly. She accused the Culture Minister, César Antonio Molina, and the press of running a smear campaign against her.

She said that Mr Molina had left her “open-mouthed” after accusing her of doing nothing during her three years in the post. “They would not have dared do this to a man,” she said. “Whatever a woman does is always wrong.” Ms Regàs told reporters that police had asked the library not to divulge information about the losses for fear of hurting the investigation, before volunteering that they had identified the culprit.

All the evidence pointed to an Argentinian researcher, she said, who was authorised by the Spanish Ambassador in Argentina and had already fled. The Spanish Ambassador promptly denied the accusation.

Experts said that whoever took the maps was not an amateur opportunist. “This is someone who knows exactly what they were doing,” Mr Crouch said. “If you’re going to steal a map from a book, it’s one of the most valuable you can take.”

Library authorities said they noticed that the maps had gone missing during a routine stock check on August 23 but did not know when they were taken. Library officials said that the thief had managed to cheat security measures that were installed in the mid1990s, thought to include CCTV cameras.

Ms Regàs said that she had been made a scapegoat for the loss, adding that other libraries around the world had suffered similar thefts.

The National Library has been hit by thieves before. In 1988 police recovered 200 stolen books, dating from the 16th and 18th centuries, from a collector’s house.

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