"Previously having been exposed as a violator of those sanctions, 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 Preet Bharara, the US attorney for Manhattan.

The US attorney's office in Manhattan announced new charges on Tuesday against Mr Li accusing him since the 2006 designation, which prohibited him from doing business with US companies, of using a "web" of shell companies to disguise 165 separate transactions totaling $8.5 million.

Li Fangwei and his LIMMT Economic and Trade Company have been on the US sanctions list since 2006 and 2009, respectively, for alleged business dealings with Iran.

The US has offered a $5 million bounty and filed new charges against a Chinese businessman it has accused of trying to sell ballistic missile technology to Iran, allegedly using shell companies to hide millions of dollars in transactions.

US prosecutors said they had seized $6.8 million belonging to the front companies held in correspondent bank accounts at US institutions. They are seeking forfeiture of funds held in Chinese bank accounts. The US banks were not accused of any wrongdoing.



Mr Li, who is also known as Karl Lee, was charged by New York City prosecutors in 2009 with violating US sanctions. He remains a fugitive.

The new charges are part of a concerted drive by the Obama administration to go after Mr Li's business operations. The State Department issued a $5 million reward for information leading to his arrest, while the treasury department placed sanctions on eight Chinese companies it accused of acting as his fronts.

US officials said the charges showed that the administration would continue to put pressure on Iran over its nuclear programme, despite continuing diplomatic talks.

"We will continue vigorously enforcing our sanctions, even as we explore the possibility of a comprehensive deal addressing Iran's nuclear programme," said David Cohen, a senior treasury department official.

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In 2009, following the New York charges, Mr Li told the Financial Times that his company exports "common products" to Iran and other countries and suggested the US must have been acting on false intelligence.

He added that his company had very little business with Iran after it was censured by authorities in China in 2003 and 2006 and the US froze some of its offshore assets in 2006.

According to US prosecutors, Mr Li has used the front companies to try to acquire "dual use" items from the US, China and other countries that could be used to make weapons of mass destruction or devices used to deliver them.

Mr Li was charged with conspiracy to violate the International Emergency Economic Powers Act, which makes it illegal to violate US sanctions, two counts of violating the IEEPA, money laundering conspiracy, conspiracy to commit wire and bank fraud and two counts of wire fraud. He faces decades in prison if convicted.

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The renewed effort to prosecute Mr Li comes as diplomatic talks over Iran's nuclear programare reaching a critical phase, according to diplomats. One of the most delicate issues in the talks is Iran's efforts to develop missiles that could deliver nuclear weapons.

The charges comes as the US has increased sanctions against Russians, targeting seven government officials and 17 companies with ties to President Vladimir Putin over the crisis in Ukraine.