U.S. prosecutors secured an indictment against a Chinese company for conspiracy to commit economic espionage and other charges in a widening case over the alleged theft of industrial secrets from chemical giant DuPont.

Pangang Group, which was a state-owned steel manufacturer in Sichuan province, worked with a California businessman and others to obtain several valuable trade secrets from DuPont, according to the indictment unsealed on Wednesday.

Three of Pangang's subsidiaries are also named in the indictment, along with a Chinese citizen who worked for that company. Attempts to reach Pangang were not immediately successful on Wednesday.

The United States has identified industrial spying as a significant and growing threat to the nation's prosperity. In a government report released last November, authorities cited China as the world's most active and persistent perpetrators of economic espionage.

The California businessman, Walter Liew, has already been in custody for several months on witness tampering charges related to the DuPont allegations. Liew and his wife, Christina, also face charges of conspiracy to commit economic espionage and other charges in the latest indictment, handed down by a Northern California grand jury.

Lawyers for Walter and Christina Liew could not immediately be reached for comment. Tom Nolan, a lawyer for Walter Liew, has previously maintained that his client only possessed publicly available information, not trade secrets from DuPont.

Liew, a U.S. citizen, allegedly paid a former DuPont engineer for assistance in designing chloride-route titanium dioxide, also known as TiO2, according to the indictment. DuPont is the world's largest producer of the white pigment used to make a range of white-tinted products, including paper, paint and plastics.

In a court filing last week, prosecutors detailed Liew's alleged links with the Chinese government. They named, as one of the Chinese representatives who once met with him, a high-ranking Communist Party official who later became a member of the Politburo.

The case in U.S. District Court, Northern District of California is United States of America vs. Walter Liew, Christina Liew et al., 11-cr-573.

(Reporting by Dan Levine; Editing by Lisa Von Ahn and Richard Chang)