LIMA, Peru — A Peruvian archaeologist is hurling allegations of plagiarism and intellectual plunder at American colleagues over a barren desert landscape where a mysterious culture built pyramids nearly 5,000 years ago.

Peru's government and some U.S. researchers have lined up firmly behind Ruth Shady, who has long researched the ruins of Caral, the oldest known city in the Americas. She contends that Americans Jonathan Haas and Winifred Creamer lifted conclusions from her work to advance their own broader study, published last month in the prestigious science journal Nature.

The article, based on radiocarbon dating of samples taken in three Peruvian valleys known collectively as the Norte Chico, attracted worldwide news coverage. The Chicago-area husband-and-wife team documented more than 20 major residential centers with platform mounds and pyramids along the Peruvian coast. The article showed that Caral was part of a complex society that flourished at the same time the pyramids of Egypt were being built.

"The truth is these people are Machiavellian," Shady said. "The interpretations that they published in Nature, having to do with the theory of development of complex societies, was plagiarized from our 10 years of work."

Haas, of the Chicago Field Museum, angrily denied the charge, initially made in a statement Shady issued about two weeks ago.

"If you look at our article that came out in Nature, she is appropriately cited. She is cited five times," he said this week in a phone interview from his research center in Barranca, 100 miles north of the capital, Lima.

Two of Shady's earlier papers on Caral were referenced, but she was not mentioned by name in the Nature article.

"We're simply saying that we've done some interesting new research and that it shows that it's actually a region, not a single site," Haas said. "It dates back to 3000 B.C. and lasted for 1,200 years. That's a pretty big story."

He said the dispute stemmed from 2001, when he and his wife co-authored a scientific paper with Shady that carbon-dated plant fibers from Caral's main pyramid to 2627 B.C.

Shady was furious because international media coverage incorrectly focused on the American couple as the discovers of Caral, Haas said, when in fact Shady had been doing research there years before they briefly joined her project.

He said when the Nature article came out, even Peruvian news media mistook it for Caral, but insisted that he and Creamer shouldn't be held responsible for the journalistic misinterpretation.

"We don't want to take anything from Ruth. The last thing we want is responsibility for the work that's going on at Caral," Haas said.

He acknowledged that his Peruvian research assistant, Alvaro Ruiz, a co-author of the Nature article, had been Shady's student. But he dismissed as "ludicrous" her allegation that the couple "lured" Ruiz with money and a scholarship at Northern Illinois University, where Creamer is based, to usurp Shady's research and theories.

The director of Peru's National Institute of Culture, Luis Guillermo Lumbreras, sent a letter dated Jan. 6 to the Society for American Archaeology requesting its ethics committee investigate. Peru's Education Minister Javier Sota Nadal said he and Foreign Minister Manuel Rodriguez were pressing their concerns about the dispute through Peru's embassy in Washington.

Anthropologist Betty Meggers, of the Smithsonian Institution, sent a letter Jan. 3 to the National Geographic Society titled "Unethical behavior of grantees Jonathan Haas and Winifred Creamer." Haas confirmed the complaint by Meggers, which Shady posted on the Internet.

Michael Moseley, a professor at the University of Florida, said Haas and Creamer were creating a "detrimental" situation for "many of us who have worked down there for many, many years and tried to develop good relationships."

"Basically what Haas and Creamer have done is move into several valleys immediately north of Shady's research area and they've expanded the database on these early monuments," Moseley said. "The problem has been that Haas and Creamer have tended to present the results as their own without very adequate citing of Shady's really pioneering research."