The report, released Thursday by two American human rights organizations, raises serious questions about the implications of U.S. military aid to Colombia. The United States has provided more than $7 billion in mostly military aid to Colombia since 2000 for fighting drugs and counterinsurgency - making it the largest recipient of U.S. military aid after Israel.

The army is accused of killing civilians and presenting them as guerrillas killed in combat to pump body counts. The Colombian military faces significant political pressure to produce concrete results in its war against the the FARC (Revolutionary Armed Forces of Colombia), the country's left-wing guerrilla insurgency.

Many point to the macabre practice - euphemistically known as producing a “false positive” - as a result of an unofficial incentive-based system that rewards high numbers of combat kills with job perks and promotions. Colombia's attorney general's office is investigating more than 2,000 alleged cases of false-positives committed by the armed forces.

The report was based on a two-year study using records of 3,000 reported extrajudicial killings since 2002 and lists of 500 military units approved to receive U.S. assistance. It found that in regions that received the largest increases in U.S. aid, the number of reported extrajudicial killings surged 56 percent on average in the four years surrounding the aid boost. When U.S. assistance was withdrawn or reduced, the number of army killings of civilians dropped.

The Fellowship of Reconciliation and the U.S. Office on Colombia published the report. The U.S. Embassy declined to comment.

Most U.S. military aid has come in the form of equipment, training, intelligence and anti-narcotics efforts such as the fumigation of coca crops.

At the heart of U.S.-backed efforts is the region of Meta, a traditional guerrilla stronghold of vast savannah and river networks. Parts of Meta were demilitarized as part of the failed 1999-2002 peace talks between the government and the FARC. The guerrillas used a cease-fire to strengthen their presence in the region. As a result, it became a priority for President Alvaro Uribe’s government to recover the territory from the guerrillas and Meta received a massive injection of government troops.

While the Colombian government has been credited with restoring security to many parts of the country, many residents interviewed in various hamlets and towns in Meta said their security situation has worsened as a result of the military presence. They complain that the armed forces indiscriminately accuse all inhabitants of being, or collaborating with, guerrillas simply because they live in a formerly guerrilla-controlled area.

As a result, “the impact of the war for the civilian population has increased,” said Edinson Cuellar, a lawyer with the Orlando Fals Borda Lawyers Collective, a group that monitors human rights violations in the region.

In a hamlet in Meta’s interior, military troops patrol through the intersection of a pot-holed dirt road lined by mostly abandoned homes. Many have fled over the last several years as a result of violence or because of worsening economic conditions.

Meta's economy used to revolve around cocoa cultivation, which has fallen dramatically in the area with eradication efforts. The U.S. government has invested tens of millions of dollars in pilot projects in the region - to mixed reviews - aimed at fostering social and economic development while improving security.

Behind her home, Beatriz Villegas, 31, tells her story in a hushed voice. In 2006, neighbors went looking for her brother, a farmer living in a different settlement. But army soldiers who had landed by helicopter didn’t allow them onto her brother’s farm. Once the military left, neighbors found his I.D. card on the counter of his ransacked home and a pair of bloody gloves and his rubber boots strewn on the ground next to the house.

Villegas and her mother traveled to La Macarena to look for his body. The local Rapid Deployment Force units - who witnesses said carried away her brother's body - have all been vetted to receive U.S. assistance since 2005, according to the report.

There, in the local office of the attorney general, Villegas leafed through photos of her brother splayed on the ground, his leg destroyed with a bullet wound. She was told he had been brought in by the military, recorded as an unidentified guerrilla killed in combat and buried in the local cemetery.

But Villegas says her brother was not a member of the militia. There has been no investigation into her brother’s death and Villegas is confounded by it. “Because he was a good guy, very hard-working … a clean guy,” she said. “Those who are guilty should be punished, because he didn’t have anything to do with the war they are fighting.”

It appears Villegas’ brother is but one false-positive in the region. Since 2002, there have been 256 civilian killings reported in southern Meta and neighboring Guaviare department, according to the report. The report found that following a rise in U.S. assistance in 2005-2006 to the Seventh Brigade in charge of that area, the number of reported army killing of civilians swelled by more than 600 percent.

John Lindsay-Poland, research and advocacy director for the Fellowship of Reconciliation, said there could be a host of factors behind the surges in army killings, including the general levels of violence in certain regions or stepped-up military activity. “We can’t say there is a cause -and-effect relationship,” said Lindsay-Poland.

The report's authors argue that their findings demonstrate a violation of the Leahy Law, which requires the U.S. government to vet foreign forces before receiving aid to ensure they are not guilty of severe human rights abuses.

Lindsay-Poland said a stricter implementation of the law would "require suspension of assistance to virtually all military brigades and most mobile brigades."