The nearly $5 billion U.S. aid package known as Plan Colombia failed to meet its goal of halving illegal narcotics production in this Andean nation, says a U.S. congressional report released Wednesday.

The General Accounting Office report does, however, note that the mostly military assistance helped Colombia markedly improve security, with kidnapping and murder rates falling and the armed forces greatly diminishing the leftist rebel threat.

Its release comes as U.S. officials make it clear that aid for Colombia, an estimated $657 million in fiscal 2008, will now be trimmed because of the U.S. financial crisis.

A widening scandal over army killings of civilians to boost body counts that cost Colombia's army chief his job this week could, additionally, impact U.S. aid to the nation.

President-elect Barack Obama is among U.S. Democrats who have expressed concern over state involvement in human rights violations in Colombia's long-running conflict.

Despite record aerial eradication, coca cultivation rose by 15 percent in this Andean nation during Plan Colombia's 2000-2006 run, the report by the U.S. Congress' research arm says.

It added that cocaine production rose by less — 4 percent — because eradication efforts forced growers to more widely disperse their crops, contributing to lower yields.

Opium cultivation and heroin production did, however, decline by 50 percent over the period.

"I think it's very, very important that a U.S. agency has now said that the U.S. drug war has failed in Colombia," said Adam Isacson of the Center for International Policy, a liberal Washington, D.C. think tank.

Colombia remains the source of 90 percent of the cocaine in the United States and most of the heroin consumed east of the Mississippi river.

The GAO report was requested by Vice President-elect Joseph Biden, who chairs the Senate Foreign Relations committee, and offers recommendations for aid cuts including turning over to the Colombians operation of key military aviation units.

Its authors recommend U.S. and Colombian officials "develop a joint plan for turning over operational and funding responsibilities for U.S.-supported programs to Colombia."

Over what period remains unclear, and the report cautions that Colombia's security gains are "not irreversible" as long as rebels remain a threat.

The ranks of Colombia's military and police rose to 415,000 from 279,000 from 2000-2007, the report notes, while the leftist Revolutionary Armed Forces of Colombia diminished by half to about 8,000 fighters.

Defense Minister Juan Manuel Santos said Wednesday that U.S. Democrats are divided over whether to change the roughly 2-to-1 balance of military versus economic aid.

He said he hoped pending discussions with yet-to-be named members of Obama's administration would result in "cuts that are the fewest painful possible."

Plan Colombia was announced in 1999 and was an initiative of then-President Andres Pastrana and U.S. President Bill Clinton.

Pastrana told The Associated Press on Wednesday that he was worried about potentially crippling aid cuts.

"Obama is going to have to think about the fact that we're combatting a common enemy, which is narcoterrorism — and that he can't leave Colombia alone."