LONDON - A group opposed to the death penalty filed a lawsuit Tuesday to try to prevent a British company from exporting a drug that could be used in the execution of an American inmate.

Reprieve, a London-based legal advocacy group and the London law firm Leigh Day & Co. are suing in the hope of forcing the government to regulate the export of sodium thiopental. The sedative, which is part of the three-drug cocktail used in lethal injections in the United States, was scheduled to be exported from Britain to Tennessee imminently, Reprieve said.

The group warned that sodium thiopental would be used in the execution of 56-year-old Edmund Zagorski, who has been convicted of committing two murders in 1983.

"All it would take to prevent the death of Mr. Zagorski and others" would be for Business Secretary Vince Cable to issue an emergency order regulating the export of sodium thiopental, said Reprieve spokeswoman Katherine O'Shea.

Cable's office did not immediately respond to a request for comment.

Sodium thiopental has historically been used as a general anesthetic, but is also the first of three drugs given during the lethal injection process for death row prisoners. The U.S. has a shortage of sodium thiopental and multiple states have halted or slowed the pace of lethal injections while searching for alternative sources of the drug.

Last week, Arizona Chief Deputy Attorney General Tim Nelson told The AP the state obtained from Britain the sodium thiopental used to execute an inmate. The Tennessee Department of Corrections said in a memo that it would buy the drug from a British company and that it would be shipped very soon, Leigh Day lawyer Richard Stein said.