A US judge on Thursday sentenced Russian "merchant of death" arms smuggler Viktor Bout to 25 years in prison for conspiring to sell a massive arsenal to anti-American guerrillas in Colombia.

Bout, 45, has been accused of selling arms to despots and insurgency groups embroiled in some of the world's bloodiest conflicts and was the inspiration for the arms smuggler played by Nicolas Cage in "Lord of War" (2005).

Prosecutors had asked for life in prison, but US district judge Shira Scheindlin decided to give Bout the minimum required sentence of 25 years on one count and 15 years for each of the three other counts of which he was found guilty, to run concurrently.

"Twenty-five years is sufficient," Scheindlin said, citing the "unique circumstances" of his case and the fact that it was the result of a sting operation.

"He embraced an opportunity presented to him to make money, but didn't seek it," she said, adding there was "no evidence that he was looking to get actively involved with a terrorist organization."

She handed down the sentence after the mustachioed Bout, dressed in a light green prison suit, stood before her and, dramatically pointing to the packed court room, insisted he was innocent.

"I am not guilty," he said, speaking in Russian through a translator. "I never intended to kill anyone and I never intended to sell arms to anyone."

"God knows the truth," he said firmly.

His wife Alla and daughter Lisa, 17, who wrote a letter to the judge proclaiming her father's innocence, were seated in the second row in the courtroom. Journalists filled a section of the court normally reserved for juries.

The sentencing had been delayed twice, with Bout's lawyer demanding more time to prepare his request for leniency and accusing prosecutors of "outrageous government conduct" in allegedly entrapping the Russian.

Bout was eventually extradited to the United States and convicted in November on four counts of conspiring to sell missiles to terrorists and to kill US troops.

"Today's sentence is a fitting coda for this career arms trafficker of the most dangerous order," said US Attorney Preet Bharara.

The head of the US Drug Enforcement Administration, Michele Leonhart, said Bout's crimes "represent the worst case scenario for modern law enforcement -- the merger of criminal international narcotics cartels with their terrorism enablers."

But Bout's defense attorney has called the prosecution a "disgrace," accusing US agents of entrapment and denying that his client ever committed any crime against the United States or its citizens.

Bout was "targeted not for investigation, for this was not an investigation -- it was a foregone conclusion," attorney Albert Dayan wrote in a letter Wednesday to Scheindlin.

US agents posing as members of the leftist Revolutionary Armed Forces of Colombia (FARC), a US-designated terrorist organization, lured Bout to Thailand from his native Russia, where he was under government protection.

In Bangkok, they pretended to be seeking infantry and anti-aircraft missiles to shoot down American pilots helping the Colombian military.

In secretly taped conversations, Bout said he could supply the weapons. However, his lawyer said in court it was a charade to further his real goal, which was simply to sell two cargo planes.

Bout is widely believed to have been the world's biggest black market arms dealer in the post-Cold War period, specializing in arming African warlords and dictators.

"The sentencing of Viktor Bout sets a global precedent in the battle to put illegal arms traffickers out of business," said Kathi Lynn Austin, executive director at Conflict Awareness Project.

"However, we should not fool ourselves that there are not others out there in line to fill his shoes," she added in a statement, calling for a strong international arms trade treaty.

Bout says he worked exclusively as a private air transporter -- although sometimes carrying legal shipments of arms.

He is not wanted for any crime in his native Russia, which has called for his return and cast doubt on the fairness of his conviction.

Scheindlin ruled in February in favor of an appeal by Bout's lawyers to let him out of solitary confinement for the first time in 15 months.