The report said coca production increased despite eradication efforts
A $6bn US aid plan for Colombia has failed to reach its target of halving drug production in the Andean country, a Congressional report says.
Despite record aerial eradication, coca cultivation in Colombia rose by 15% between 2000 and 2006, the report says.
But the US programme - Plan Colombia - has helped reduce Colombia's kidnapping and murder rates while diminishing the threat from left-wing rebels, it adds.
US officials have said aid will be trimmed due to the financial crisis.
Bogota receives around $600m a year in US aid to combat drugs trafficking.
The report recommends aid cuts, advising US and Colombian officials to "develop a joint plan for turning over operational and funding responsibilities for US-supported programmes to Colombia".
The report was requested by Vice-president elect Joe Biden, chairman of the Senate Foreign Relations committee, and was prepared by the General Accounting Office.
US aid for Colombia amounted to around $650m in 2008
President-elect Barack Obama is among the US politicians who have expressed concern over human rights violations in Colombia's long-running conflict.
Despite Plan Colombia, the country remains the world's top cocaine producer and is reportedly the source of 90% of the drug in the US.
An initiative formulated by former US President Bill Clinton and his Colombian counterpart Andres Pastrana, Plan Colombia was announced in 1999.
It involves the training of Colombian forces and the provision of equipment and intelligence to combat drug-traffickers and eliminate coca crops.