|Bout was arrested in a US sting operation in 2008, and has been fighting extradition to the US ever since [Reuters]
Viktor Bout, a suspected Russian arms dealer, has been extradited to the United States after Thai authorities cleared the transfer days before his detention was due to expire.
Bout was flown out of Bangkok on a special US jet on Tuesday, Thai police said.
He faces charges of terrorism linked to the trafficking of weapons to conflict zones in Africa, South America and the Middle East.
Abhisit Vejjajiva, Thailand's prime minister, told reporters earlier on Tuesday that his cabinet had agreed to uphold a court decision to allow Bout, alleged to be one of the world's biggest arms dealers, to be sent the US to face trial.
The 43-year-old former Soviet air force officer, dubbed the "Merchant of Death", was arrested in Bangkok in March 2008 as part of a US-led sting operation.
Bout's lawyer has 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.
The Russian foreign ministry described the extradition an illegal act which had no justification and was prompted by unprecedented US pressure on Thailand.
"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.
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 dentention 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, has been held in a Thai maximum-security prison since his arrest.