WASHINGTON • The U.S. government spent over $3 billion in recent years to combat drugs in Latin America, more than half of it to private contractors for planes, surveillance and training.

But a year-long investigation by a Senate subcommittee found little oversight over spending, lost contracts and $840 million in no-bid contracts, according to a report released this morning.

"It's becoming increasingly clear that our efforts to rein in the narcotics trade in Latin America, especially as it relates to the government's use of contractors, have largely failed," said Sen. Claire McCaskill, who chairs the Senate Subcommittee on Contracting Oversight.

"Without adequate oversight and management, we are wasting tax dollars and throwing money at a problem without even knowing what we're getting in return," McCaskill, D-Mo., added in a statement.

McCaskill reached her conclusions after investigators examined Pentagon and State Department anti-drug spending in Colombia and other Latin American nations from 2005-2009.

During that time, the report says, contract spending increased by one-third -- from $482 million to $636 million -- even though the government has no system in place to evaluate whether contractors do what they're paid for.