By Jonathan Stempel

NEW YORK (Reuters) - A U.S. appeals court on Monday denied a new trial for Viktor Bout, a Russian arms trafficker serving a 25-year prison sentence for plotting to sell missiles to people he thought were Colombian rebels.

The 2nd U.S. Circuit Court of Appeals in Manhattan said a trial judge did not abuse her discretion by refusing to dismiss Bout's indictment and rejecting his claim that new evidence justified overturning his November 2011 conviction.

Bout, 49, was convicted of conspiring to kill U.S. soldiers by agreeing to sell arms to U.S. Drug Enforcement Administration informants posing as members of the Revolutionary Armed Forces of Colombia, or FARC.

The U.S. government has called FARC a foreign terrorist organization.

In seeking a new trial, Bout said he could not have conspired with former business associate Andrew Smulian, who testified against him at trial, because Smulian already had been recruited as a DEA informant.

But the appeals court said the evidence suggested merely that the agency "saw Smulian as a way to get to Bout."

Alexey Tarasov, Bout's lawyer, said he "respectfully disagreed" with the decision and will review legal options with his client. He said these include a possible appeal to the U.S. Supreme Court, or a possible return of Bout to Russia.

The office of U.S. Attorney Preet Bharara in Manhattan did not immediately respond to a request for comment.

An earlier appeal by Bout was dismissed by the 2nd Circuit in September 2013.

Bout, the subject of the 2007 book "Merchant of Death," was arrested in Bangkok in March 2008 following a global sting operation. He is now in a prison in Marion, Illinois, and eligible for release in January 2030.

The case is U.S. v. Bout, 2nd U.S. Circuit Court of Appeals, No. 15-3592.

(Reporting by Jonathan Stempel in New York; Editing by Bill Trott and Grant McCool)