Thailand defended the Appeal Court's decision yesterday to extradite Viktor Bout - the Russian "Merchant of Death" - to the United States, which made Moscow very angry.
"We have to make them understand that the court ruling was in line with facts and justice, not under the political influence of any party," Prime Minister Abhisit Vejjajiva said.
The arms smuggler, meanwhile, said he would prove his innocence in the US.
"We will face the trial in the United States and win it," Russian news agency RIA Novosti quoted Bout as saying after the verdict.
Bout, said to have inspired the 2005 Hollywood film "Lord of War" starring Nicolas Cage, has been fighting extradition since he was arrested in March 2008 in Bangkok as part of a sting operation involving US agents posing as Colombian rebels.
He faces a maximum life sentence if convicted in the United States on charges including conspiracy to kill US nationals and providing material support or resources to a foreign terrorist organisation.
Bout's young daughter broke down in tears after the ruling was delivered, while his wife Alla said it was "unfair" and had been made under pressure from Washington.
Judge Jitakorn Patanasiri announced: "The court will detain him for extradition to the US."
The court ordered Bout's extradition within three months, overturning a lower court's ruling last August that rejected Washington's request that he be tried in the United States. No further judicial appeals are possible, according to the Extradition Law.
The ruling is a victory for the administration of US President Barack Obama, which summoned the Thai ambassador this week to "emphasise that this is of the highest priority to the United States", State Department spokesman PJ Crowley said.
However, Russian Foreign Minister Sergey Lavrov called the court decision "unlawful and political". Without mentioning the United States, he said the ruling was influenced by "very strong outside pressure".
Abhisit acknowledged both sides had pressured Thailand, but insisted the court's decision was in accordance with law and fact.
Experts say Bout has been useful for Russia's intelligence apparatus, and Moscow does not want him going on trial in the United States.
Bout, a 43yearold former Soviet Air Force officer, is reputed to be one of the world's most prolific arms dealers. He has allegedly supplied weapons that fuelled civil wars in South America, the Middle East and Africa, with clients including Liberia's Charles Taylor and Libyan leader Mu'ammar Gadhafi and both sides of the civil war in Angola.
Pavel Felgenhauer, an independent Moscowbased military analyst, called Bout a "prize catch" for Washington and an embarrassment for Moscow.
"The activities he was performing involved a lot of Russian government officials. The information he has, many parties want to keep under wraps," he said.
The US could secure key military intelligence not only on Russia, but on other former Soviet states where Bout was operating, he said, adding that if Bout were to accept a plea bargain, "he could really start to sing".