Bout, a former Soviet air force officer, is accused of peddling weapons to some of the world's most violent groups.

The attempt by US courts to extradite Bout comes amid fears he could soon be released by a Thai court almost two years after his March 2008 arrest.

He was arrested in Bangkok, the Thai capital, after he allegedly agreed to supply missiles to Colombian rebels.

But judges said last August that they could not extradite him because the Thai government had not listed  the Revolutionary Armed Forces of Colombia (Farc) as a "terrorist" organisation.

The Thai governmen has challenged that ruling, with a decision expected soon, but the country's attorney-general's office said on Thursday that the new cases had now changed the situation.

New charges

The new charges target Bout and Richard Ammar Chichakli, his alleged co-conspirator, over alleged attempts by the two men to buy two aircraft from US-based companies in violation of economic sanctions.

Chichakli is a US citizen and has assisted in Bout's financial management of his network of aircraft companies since at least the mid-1990s, the US prosecutors office in New York said.

Lak Nitiwatvichan, Bout's lawyer in Thailand, said the latest fraud charges would not affect the current case concerning the missiles and the Farc.

"This has nothing to do with the current case," Lak said.

"The US has tried every possible way to get Bout extradited."

Bout has continually protested his innocence, insisting he was the boss of a legitimate air cargo firm.

He has been held at a maximum-security prison outside Bangkok since his arrest.