Viktor Bout, 42, was arrested in Bangkok in March last year during a sting operation led by U.S. agents. The United States accuses Bout of conspiring with others to sell millions of dollars' worth of weapons to the Revolutionary Armed Forces of Colombia (FARC).
"The Russian Foreign Ministry is acting strictly in line with international law in relation to the criminal case against Viktor Bout. Russia is not interfering with the trial, but will continue to provide legal support to Bout," Viktor Nesterenko said on Thursday.
The diplomat was commenting on Thai and Western media reports accusing Russia of applying pressure on Thai judicial and executive authorities during the trial.
"We regard these allegations as pure provocation aimed at presenting the Bout legal case as a political affair and fueling tensions both in Russian-Thai and Russian-U.S. relations," Nesterenko said.
A Thai court held another round of hearings on Bout's extradition to the United States on March 17-18, and set the next hearings for April 29.
Bout, a former officer in the Russian army, faces a life sentence if extradited and tried in a U.S. court. However, Thai authorities earlier announced that they would not press charges against him.
Western law enforcement agencies consider Bout to be "the most prominent foreign businessman" involved in trafficking arms to UN-embargoed destinations, including the Democratic Republic of Congo and Angola.
UN reports say Bout set up a network of more than 50 cargo aircraft around the world to facilitate his arms shipments, earning him the nickname "merchant of death."
In an interview published in a Russian newspaper in October, Bout said Washington fabricated charges against him after he had refused to work as an informant.