The Russian foreign ministry says it will work to bring home Bout, known as the 'merchant of death', who faces jail in the US

Russia has lashed out at the United States for its conviction of the arms dealer Viktor Bout and said it would work to bring home the notorious "merchant of death".

Bout faces between 25 years and life in prison after being found guilty on Wednesday of four counts of conspiracy to sell weapons to purported Colombian rebels with the aim of killing US citizens.

"Our goal is to achieve his return to the motherland," the foreign ministry spokesman Alexander Lukashevich said in a statement.

Lukashevich accused US authorities of illegally extraditing Bout from Thailand following his arrest during a US sting operation in Bangkok in 2008 and of "purposefully creating a negative environment that prevented the objective consideration of facts" during the trial. He said that Bout, a Russian citizen, had been held in "unnecessarily harsh conditions".

"All this calls into question the very foundation on which the charge was built and, accordingly, the validity of the judicial decision," he said.

Russia had loudly objected to Bout's arrest and fought hard in a Thai court to prevent his extradition and subsequent trial in New York. Bout built his reputation as a "merchant of death" by conquering the global arms trade in the wake of the collapse of the Soviet Union, one of the world's most heavily armed entities. His relations with the Russian government remain a mystery and he has denied serving as a Soviet army officer in Mozambique in the 1980s at the same time that Igor Sechin, a deputy prime minister and close ally of Vladimir Putin, was also serving there.

Bout pleaded not guilty and did not testify in the trial.

Bout's wife, Alla, told Russian state-run television that when she visited her husband in prison last week, she told him: "You know, no matter what happens, don't give up, because this is not the end of the story."

The conviction comes as the US and Russia struggle to keep their "reset" in relations afloat. Russia reacted angrily last month to a US state department decision to ban Russian officials linked to the death in prison of the lawyer Sergei Magnitsky, drawing up its own list of banned US officials in response. In the US, the reset has all but fallen off the agenda as the president, Barack Obama, focuses on the economy before the presidential election while US Republicans dub the policy a "disaster".

Bout's conviction has been widely denounced inside Russia. Leonid Slutsky, deputy head of the Duma's international affairs committee, told Interfax news agency it was a "typical American agitation".

"Out of Bout they made a kind of evil genius villain, carrying out some sort of evil that got its start in Russia," he said. The MP Andrei Klimov told the news agency the case was "a political order".

Bout is due to be sentenced in February.