Bout was arrested in a US sting operation in 2008, and has been fighting extradition to the US ever since [Reuters]
Sergei Lavrov, the Russian foreign minister, has said his country would support suspected arms dealer Victor Bout "by all means" and called his extradition to the United States an "extreme injustice."
Bout, a Russian national, arrived in New York on Wednesday to face charges in the US, after Thailand backed a US request for his extradition following a long legal battle.
The 43-year-old former Soviet air force officer, dubbed the "Merchant of Death," faces accusations of trafficking arms since the 1990s to dictators and conflict zones in Africa, South America and the Middle East.
Bout had been fighting extradition since he was arrested in March 2008 in Bangkok in a US-led sting operation.
Abhisit Vejjajiva, the Thai prime minister, cleared the extradition, despite Russia saying it was illegal and could undermine US-Russian ties.
Bout was flown to from Bangkok to New York on Tuesday on a small, chartered US aircraft, a spokeswoman for the Drug Enforcement Administration said.
Bout's lawyer had condemned the extradition. "This is a judicially illegal decision because the Thai court never reviewed the second US extradition request concerning (Viktor) Bout," Viktor Burobin told a Russian news agency.
"Thailand has been stuck between two massive powers, the US and Russia," Al Jazeera's Aela Callan, reporting from Bangkok, said.
"He says he is innocent and has been set up. Whatever the truth is about Viktor Bout, we are going to see more allegations dragged through the courts."
Bout runs a network of air cargo companies in the Middle East, Africa, Eastern Europe and the US.
US officials allege Bout has used this network to move weapons around the world since the 1990s.
"Viktor Bout has been indicted in the United States, but his alleged arms trafficking activity and support of armed conflicts in Africa has been a cause of concern around the world. His extradition is a victory for the rule of law worldwide," Eric Holder, the US attorney general, said in a statement.
"Long considered one of the world's most prolific arms traffickers, Mr. Bout will now appear in federal court in Manhattan to answer to charges of conspiring to sell millions of dollars worth of weapons to a terrorist organization for use in trying to kill Americans," Holder said.
According to the UN and the US treasury department, he has sold or brokered arms that have helped fuel wars in Afghanistan, Angola, the Democratic Republic of Congo, Liberia, Rwanda, Sierra Leone and Sudan.
He is accused of conspiring to sell weapons to the Revolutionary Armed Forces of Colombia (Farc), that country's largest rebel group and considered a terrorist organisation by the US.
Bout has denied the allegations against him, and his detention has been a bone of contention between US and Russian authorities.
Moscow has repeatedly suggested that proceedings against Bout are politically motivated and has called for him to be repatriated.
Moscow's aggressive lobbying for his release has fuelled speculation he was receiving protection from Russian authorities who had made no apparent attempt over the years to interfere in his alleged operations.
Russian authorities appeared to have been taken by surprise by the extradition. "We never officially received this information. We never received any notes or telephone calls," Andrei Dvornikov, the head of the embassy's consulate section, said on Tuesday.
Bout, who was inspiration for Nicholas Cage's character in the 2005 movie Lord of War, was held in a Thai maximum-security prison since his arrest.