U.S. Deputy Attorney General David Ogden told reporters he was "disappointed" by the decision of a Thai lower court in August to reject a U.S. extradition request for the Russian and was hopeful an appeals court would rule to extradite him. No date has been set for the appeal.
Bout, once dubbed the "Merchant of Death," has been accused of supplying dictators and warlords with weapons used in civil wars in South America, the Middle East and Africa.
The 42-year-old Bout was arrested in March 2008 at a Bangkok luxury hotel after U.S. agents posed as arms buyers for the Revolutionary Armed Forces of Colombia, or FARC, which Washington classifies as a terrorist organization.
After his arrest, Bout was indicted in the U.S. on charges of conspiring to sell millions of dollars worth of weapons to FARC, including more than 700 surface-to-air missiles, thousands of guns, high-tech helicopters and airplanes outfitted with grenade launchers and missiles.
The Thai court rejected the U.S. extradition request, saying Thailand considers the FARC a political movement and not a terrorist group, and that extradition could not be granted for a political offense.
In talks with Thai officials, Ogden said he "raised the issue of Viktor Bout's extradition proceeding, which is a matter of great importance to the United States. He stands charged with extremely serious crimes against Americans."
Bout has been linked to some of the world's most notorious conflicts, allegedly supplying arms to former Liberian dictator Charles Taylor and Libyan leader Moammar Gadhafi. The "Merchant of Death" nickname came in 2000 from a minister at Britain's Foreign Office who was concerned that Bout was ferrying weapons around Africa.
Bout has repeatedly denied the accusations.
Ogden's visit was the latest in a political tug of war between the U.S. and Russia, which wants to get Bout back to Moscow. Experts say Bout, a former Soviet air force officer, has been useful for Russia's intelligence apparatus, and Russia does not want him going on trial in the United States.