A federal grand jury has indicted Iranian and Chinese nationals on charges stemming from an alleged plot help Iran acquire advanced metals and other sensitive U.S. technology for its nuclear program, the Justice Department announced Friday.

The indictment of the two men was the latest to target what U.S. officials say is a global procurement network operated by Iran to obtain needed parts for its uranium enrichment plants as well as its most sophisticated missiles. At least some of materials appear to have made it to Iran, according to law enforcement officials familiar with the investigation.

While U.S. officials have prosecuted similar cases in recent years, the new indictment is considered unusual because the suspects’ shopping list involved so many highly specialized metals and parts known to be sought by Iran for its nuclear program. Among them was maraging steel, a type of high-strength metal used to make advanced gas centrifuges for uranium enrichment.

“This case confirms Iran’s persistence in seeking high-tech goods for its centrifuge program in Europe and the United States,” said David Albright, a former U.N. nuclear inspector who has studied Iran’s nuclear procurement efforts for more than a decade. “Iran remains dependent on foreign supply for many vital goods for its centrifuge program.”

The indictment, returned on Thursday by a grand jury in Washington, names as co-conspirators Paviz Khaki, an Iranian citizen, and Zhongcheng Yi, a Chinese man described as a director of a Chinese company that allegedly facilitated clandestine efforts by Iran to acquire technology and parts. Khaki was arrested in May by authorities in the Philippines following a joint investigation, and Yi is still being sought, court documents said. Two other alleged participants in the scheme were indicted but not named .

Justice Department documents allege that Khaki made numerous attempts over three years to acquire U.S.-made maraging steel and other special metals, using Yi and other Chinese nationals as middlemen. In March 2009, he also began working directly with an American citizen who he believed to be an export manager, seeking help in exporting 20 tons of maraging steel to Iran.

The export manager — actually an undercover officer — agreed to help. While the two haggled over prices and payments, Khaki acknowledged in an e-mail that there were international restrictions on the sale of maraging steel.

“You know and I know this material are [sic] limited material and danger goods,” Khaki wrote, according to the indictment.

Khaki also allegedly shopped for 20 tons of a special aluminum alloy used in centrifuges, insisting on American-made metals because he said they were of higher quality than counterparts made in China. Among his other purchases was a mass spectrometer, a device used in the nuclear industry to measure the isotopic makeup of enriched uranium. In one e-mail he specified that the device would have to be suitable for analyzing uranium hexafluoride, the uranium gas pumped into centrifuges and converted to the enriched uranium used as fuel for nuclear power plants or — with further enrichment — in nuclear bombs.

The case was investigated jointly by the Justice Department and the Homeland Security Department’s Immigration and Customs Enforcement office, which probes violations of export law. Lisa Monaco, Justice’s assistant attorney general for national security, said the indictment “sheds light on the reach of Iran’s illegal procurement networks and the importance of keeping U.S. nuclear-related materials from being exploited by Iran.”

“Iranian procurement networks continue to target U.S. and Western companies for technology acquisition,” she said, “by using fraud, front companies and middlemen in nations around the globe.”

Despite the use of informants in the United States and overseas, U.S. officials were unable to determine whether Iran obtained the maraging steel, though it did receive some of the other items it sought. Nuclear experts say Iran remains incapable of making maraging steel, which apparently accounts for the Islamic republic’s relatively slow progress in making second-generation centrifuges to replace the outmoded ones it uses.