BOGOTÁ - "There are alarming links between increased reports of extrajudicial executions of civilians by the Colombian army and units that receive U.S. military financing," John Lindsay-Poland, lead author of a two-year study on the question, told IPS.

Lindsay-Poland is Research and Advocacy Director for the U.S.-based Fellowship of Reconciliation (FOR), which presented a new report, "Military Assistance and Human Rights: Colombia, U.S. Accountability, and Global Implications", in Bogotá Thursday.

The report, produced in conjunction with the U.S. Office on Colombia (USOC), studies the application in Colombia of the so-called Leahy Law, passed in 1996, which bans military assistance to a foreign security force unit if the U.S. State Department has credible evidence that the unit has committed gross human rights violations.

The Leahy Law is one of the main U.S. laws designed to protect against the use of U.S. foreign aid to commit human rights abuses.

"If the Leahy Law was fully implemented, assistance would have to be suspended to nearly all fixed army brigades and many mobile brigades in Colombia," Lindsay-Poland said.

The report points out that most military training in Colombia is funded by the U.S. Defence Department.

Colombia, caught up in an armed conflict for nearly five decades, is one of the largest recipients of U.S. military aid in the world, along with Israel, Egypt and Pakistan.

The study reviewed data on more than 3,000 extrajudicial executions reportedly committed by the armed forces in Colombia since 2002 and lists of more than 500 military units assisted by the United States since 2000.

"We found that for many military units, reports of extrajudicial executions increased during and after the highest levels of U.S. assistance," Lindsay-Poland said.

The results were obtained by comparing the number of reports of such killings in the two years prior to the start of Plan Colombia -- the multibillion-dollar U.S. military aid package -- in 2000 with the number of killings after the launch of that counterinsurgency and anti-drug strategy.

It also found that reports of alleged killings of civilians by the army dropped when assistance was cut.

"Whatever correlation may exist between assistance and reported killings, there are clearly other factors contributing to high levels of killings. Yet, while we could not fix the causes of increased reports of killings after increases in U.S. assistance, our findings highlight the need for a thorough investigation into the reasons for this apparent correlation," the authors say.

"The U.S. government should respond to the questions raised by the report," Lindsay-Poland said.

For example, "why U.S. officials neglect their duties under the Leahy Law, not only in Colombia but in countries like Pakistan, where the situation is very complex."

The U.S. military presence in Colombia dates back to the 1940s, when leftwing guerrillas became active in the country. But it escalated to a new level in 1999 when Plan Colombia was agreed by the governments of then presidents Andrés Pastrana (1998-2002) and Bill Clinton (1993-2001).

Plan Colombia was complemented and extended in 2004 by Plan Patriot, signed by President Álvaro Uribe, whose term ends Aug. 7, and former president George W. Bush (2001-2009).

The two plans have undergone radical changes since 2009, according to Lindsay-Poland, when they reached beyond the initial aims of counterinsurgency and counternarcotics, with a view towards strengthening U.S. control in the region.

U.S. army Southern Command documents state the importance of establishing a base "with air mobility reach on the South American continent and a capacity for counter-narcotics operations until the year 2025," he said.

Uribe offered the U.S. military the use of seven bases at strategic points in Colombia, including both the Atlantic and Pacific coasts, the province of Caquetá in the Amazon jungle, and the provinces of Meta, Tolima and Cundinamarca in the centre of the country.

Lindsay-Poland and other members of FOR tried to visit the Palanquero base in Cundinamarca, one of the seven, on Wednesday. But "they did not let us in," he said. "They demanded authorisation from the U.S. Embassy. So what kind of autonomy are we talking about here?"

Furthermore, the agreement for U.S. military access to the bases has not been approved by the Colombian Congress, as required by law.

As a result, the Constitutional Court ruled the agreement unconstitutional on Jul. 22 and gave Congress one year to approve or reject it.

If the legislature ratifies the deal, the Constitutional Court will once again study it, to determine whether or not it is in line with the constitution.

The report presented by FOR and USOC coincided with the start of an investigation of reports of unmarked graves in the La Macarena cemetery, which is next to an army base, according to a Jul. 22 public hearing in that town in the central province of Meta, which was attended by opposition lawmakers and international observers, including European legislators.

At the hearing, witnesses said military helicopters flew in the remains of bodies to La Macarena, 340 km south of Bogotá. Human rights groups say the bodies were those of civilians killed by the army.

"This is happening at the end of a government marked by grave human rights violations, which have largely affected the most vulnerable groups in society, and which are reflected in the thousands of 'false positives', as the extrajudicial executions have been popularly known," Alberto Yepes, director of the Observatorio de Derechos Humanos (DIH - Human Rights Observatory), told IPS.

The scandal over the so-called "false positives" -- young civilians killed by the army and passed off as guerrilla casualties in the military's counterinsurgency campaign --broke in the press in September 2008.

Although there are no hard statistics on the number of people killed, the report by FOR and USOC puts the number at over 3,000 in the last decade.

A group that calls itself the Madres (mothers) of Soacha, a vast working-class suburb stretching south of Bogotá, has filed a complaint with the Inter-American Commission on Human Rights over the loss of their 16 sons in 2007 and 2008. The young men were recruited with the promise of jobs, but their bodies were found in morgues or mass graves hundreds of kilometres away.

Yepes said the complaint filed by the Madres de Soacha "is a way to pressure the state to modify this kind of behaviour."

While activists and groups mobilise to pressure the armed forces to live up to the constitution, "the United States should assume its responsibility through better oversight, holding (authorities in Colombia) accountable and adopting corrective measures, so the money of U.S. taxpayers does not end up financing killings in Colombia," he said.