Bangkok, Thailand (CNN) -- Suspected international arms dealer Viktor Bout waited for extradition to the United States in a Thai prison Thursday as the Ministry of Foreign Affairs processed a letter from Washington to clear the way, government officials said.
Last week, a Thai appeals court ruled that Bout could be extradited to the United States, but a second extradition request on a separate charge threatened to delay the process.
Washington filed the second case to extradite Bout, according to Thani Thongpakdi, a deputy spokesman for the Thai Ministry of Foreign Affairs, possibly as a hedge if the first ruling went against it.
The United States is now withdrawing it since Bout can't leave the country until any pending cases against him have been settled.
Sirisak Tiyaphan with the Thai Attorney General's office of International Affairs said Bout was unlikely to leave for the United States Thursday because the request was still being handled by the foreign affairs ministry.
Last week's ruling came after heavy lobbying from U.S. officials.
"We are extremely pleased that the Appeals Court in Thailand has granted the extradition of Viktor Bout to the United States on charges of conspiring to sell weapons to a terrorist organization for use in killing Americans," said a statement by acting U.S. Deputy Attorney General Gary Grindler. "We have always felt that the facts of the case, the relevant Thai law and the terms of our bilateral extradition treaty clearly supported the extradition of Mr. Bout on these charges."
Russian Foreign Minister Sergei Lavrov described the Thai appeals court's ruling as an "unlawful, political decision" that was "taken under a very strong pressure from the outside," Russian state-run news agency RIA Novosti reported.
"I can assure you that we'll do everything necessary for his return to his home country," Lavrov told reporters, according to RIA Novosti.
Bout, a former Soviet military officer, had been indicted by U.S. federal authorities on a series of charges, including counts of illegally purchasing U.S. cargo planes to ferry weapons to warring parties and regimes in Africa and the Middle East.
Thai courts had previously balked at extraditing Bout to the United States on the basis of the original charges against him, which centered on his alleged efforts to send millions of dollars worth of weapons to arm guerrilla fighters in Colombia. Last year, a Thai court rejected the U.S. government's request for extradition.
Bout was arrested in Bangkok in March 2008 after a sting operation led by agents of the U.S. Drug Enforcement Agency, posing as members of the Revolutionary Armed Forces of Colombia (FARC).
Bout, widely regarded as a prolific arms dealer, has been in Thai custody since.
Bout has repeatedly said he has not broken any laws and the allegations against him are lies.
He is accused of supplying weapons to war zones around the world -- from Sierra Leone to Afghanistan.
In February, a federal indictment charged Bout and an alleged co-conspirator with the illegal purchase of a Boeing 727 and a Boeing 737, money laundering and wire fraud.
The United States charged Bout in 2008 with agreeing to sell surface-to-air missiles, armor-piercing rocket launchers, "ultralight" airplanes, unmanned aerial vehicles, and other weapons to FARC. Justice Department officials have sought his extradition since then.
Federal authorities accused Bout of four terrorism offenses: conspiracy to kill U.S. nationals, conspiracy to kill U.S. officers or employees, conspiracy to acquire and use an anti-aircraft missile, and conspiracy to provide material support or resources to a designated foreign terrorist organization, the designation given to FARC by the U.S. State Department.
A former Soviet air force officer who speaks six languages, Bout allegedly began building his arms business as the Soviet Union disintegrated in the early 1990s. He acquired surplus Soviet planes and, according to the U.S. Treasury Department, started shipping arms and ammunition to various conflict zones.
It is widely believed that he inspired the character of Yuri Orlov, the arms dealer played by Nicolas Cage in the 2005 film "Lord of War."
CNN's Kocha Olarn and Ed Payne contributed to this report.