The United States unveiled a new indictment and slapped a $5 million reward Tuesday on the head of a Chinese man it called a "principal supplier" to Iran's ballistic missile program.

Washington said Li Fangwei, or Karl Lee, has continued to ship equipment and materials to Iran even after he and his company LIMMT Economic and Trade were first indicted and blacklisted by the United States in 2009.

The Department of Justice's new charges allege that he used China-based front companies -- some with the same address as LIMMT -- to move millions of dollars worth of payments from Iran through the US financial system.

The department said it had seized of nearly $7 million linked to the payments, claiming the money from the accounts of Chinese banks in US banks.

From 2006 to 2014, the Justice Department said, Li used front companies for more than 165 separate US dollar transactions, worth more than $8.5 million.

"Included in those illicit transactions have been transactions involving sales to US companies and sales of merchandise by Li Fangwei to Iran-based companies utilizing the US financial system," it said.

The indictment said that in 2011, via a front company, Li exported to Iran a production line for aramid fiber, which can be used for ballistic missiles and centrifuges for uranium enrichment, as well as for body armor.

He also used front companies, it said, to invoice Iranian buyers for shipments of specialized tubes, pipes and rods that can be used in developing gas centrifuges.

Such centrifuges are at the center of accusations that Iran is seeking to enrich enough nuclear fuel to arm future atomic weapons.

The money seized came mainly from US accounts of the Shanghai Pudong Development Bank, with a small portion as well from a Bank of China account.

Li was charged with violating the International Emergency Economic Powers Act, under which he is banned from the US financial system; with wire and bank fraud; and with money laundering.

"Li spun a web of front companies to carry out prohibited transactions essentially in disguise. He now stands charged with serious crimes, and millions of his dollars have been seized," said US Attorney Preet Bharara in a statement.

In addition to the new charges and reward against Li, the US blacklisted eight companies tied to him and also on a Dubai businessman, Saeed al-Aqili, accused of helping Iran skirt international controls on its oil exports.

The blacklist forbids US citizens or businesses from transactions with them and freezes any assets they may have in a US jurisdiction.

The new sanctions come even as Washington, one of the "P5+1" powers negotiating with Tehran, have loosened general sanctions on the country's economy as an incentive to make progress on halting what is believed is Iran's effort to develop nuclear weapons.

After a temporary deal on the issue was struck in November, the group -- United States, Britain, France, China and Russia plus Germany -- is now seeking a permanent accord before a July 20 deadline.

"As we have made clear, we will continue vigorously to enforce our sanctions, even as we explore the possibility of a comprehensive deal addressing Iran's nuclear program," said Treasury Under Secretary for Terrorism and Financial Intelligence David Cohen in a statement.