Pfizer hired investigators to dig up dirt on Nigeria's then-attorney general early last year in an effort to pressure him to drop a $6 billion lawsuit against the company, according to a classified U.S. diplomatic cable.

The high-profile litigation, which stemmed from a 1996 drug experiment conducted on perilously ill children, was settled privately after the meeting that led to the April 20, 2009, cable.

The cable was released last week by the anti-secrecy Web site WikiLeaks and represents just the latest twist in the case's 14-year saga. In a statement, Pfizer called the new allegations "simply preposterous."

The Pfizer drug trial, whose tale has been compared to the plot of the Academy Award-winning movie "The Constant Gardener," has become notorious since its details were first made public in a 2000 investigative series in The Washington Post, and in a follow-up investigation in 2006 that led to homicide charges against the company.

In 1996, Pfizer's researchers selected 200 children at an epidemic hospital in Nigeria, then gave about half of them an untested oral version of the antibiotic Trovan. The other children were given a comparison drug. Researchers did not obtain signed consent forms, and medical personnel said Pfizer did not tell parents their children were getting an experimental drug. Pfizer's lead investigator later acknowledged that he personally created and backdated a key ethics approval document.

Eleven children died during the trial and others suffered disabling injuries. Pfizer said it broke no laws and that the deaths and other problems resulted from meningitis.

Nigerian officials brought criminal and civil charges in 2007, one set filed by state officials and the other $7 billion case brought by federal authorities.

The 2009 cable, classified as "confidential," says that Pfizer's country manager, Enrico Liggeri, met with U.S. officials in Abuja to discuss the cases.

"According to Liggeri," the cable says, "Pfizer had hired investigators to uncover corruption links to federal attorney general Michael Aondoakaa to expose him and put pressure on him to drop the federal cases. He said Pfizer's investigators were passing this information to local media.

"A series of damaging articles detailing Aondoakaa's 'alleged' corruption ties were published in February and March. Liggeri contended that Pfizer had much more damaging information on Aondoakaa and that Aondoakaa's cronies were pressuring him to drop the suit for fear of further negative articles."

Aondoakaa told the Guardian, the British newspaper that first reported on the cable, that he knew nothing about Pfizer's attempts to investigate him.

The Nigerian state of Kano settled with Pfizer for $75 million in July 2009. Details of the federal settlement were never reported.

A Pfizer representative in a phone interview Friday declined to discuss specifics of the cable or Liggeri's alleged comments. In its written statement last week, Pfizer said it negotiated the confidential settlement with the federal government "in good faith and its conduct in reaching that agreement was proper." Pfizer said it had agreed to pay the legal fees and expenses incurred by the federal government in the litigation and no payment was made to the federal government of Nigeria itself.

According to the cable, Liggeri also told U.S. officials that the lawsuits were "wholly political in nature," and that the humanitarian group Doctors Without Borders also gave children Trovan. Officials with the organization said that is not the case, and other records suggest that only Pfizer would have had access to Trovan at the time.