"The court ruling was made today morning, and it was negative," Tarasov said.
"We find the ruling unjust and disagree with it," he said.
Following the US court's ruling, Russia's Foreign Ministry said in a statement Monday that Moscow was disappointed with the ruling, calling Bout's trial "biased." It said Russia would keep doing its utmost for Bout's expedient return to his homeland, working with both the outgoing and incoming US administrations.
Bout was arrested in Bangkok in 2008 in a joint operation between Thai and US authorities, who accused him of conspiring to kill Americans by allegedly agreeing to supply Colombian militants with weapons.
Moscow has said that the case has been politicized and has repeatedly called on Washington to release the Russian citizen, who is serving a 25-year sentence in the United States.