The dead bodies of ten policemen and an informant, riddled with 150 bullets, has highlighted corruption among the armed forces in Colombia.

The men suspected of carrying out the expertly planned and professionally executed ambush are alleged to be members of an elite army unit, which it is claimed is in the pay of one of the country's top drug lords.

Just last week four members of an elite anti-kidnapping unit were arrested - for kidnapping. Their alleged victim, a local businessman, is believed to have been executed.

"I had the impression that the human rights abuses, if inevitable in every army throughout the world, weren't a real problem in Colombia," said Mario Iguaran, the country's attorney-general. "Now I have my doubts."

A total of 15 soldiers, including a colonel, have been arrested in connection with police killings in Jamundi, near the city of Cali, just over a month ago.

Their story that the police were killed in a tragic friendly fire incident has been rejected by Mr Iguaran after forensic evidence showed that many of the police were killed at point-blank range and that the informant took just one bullet to the back of the head.

A witness also heard the police officers begging for their lives. "This was not a mistake, it was a crime - a deliberate, criminal decision," insisted Mr Iguaran. "The army was doing the bidding of drug traffickers."

Sources within the US Embassy agreed with the attorney- general. The police, on anti- narcotics operations, were receiving up to two tonnes of cocaine belonging to Diego Montoya, alias "Don Diego", one of America's most wanted with a £2.7 million bounty on his head.

Yet this incident is just one of many that have rocked the armed forces.

Last week the trial of 147 soldiers began. They shared out more than £20 million they found in a guerrilla hide, the proceeds of drugs sales and kidnap ransoms. The vast majority have deserted with their fortunes.

The United Nations is also investigating charges that soldiers have "disappeared" men they suspected of having links to the guerrillas.

The men, last seen in the presence of soldiers, later turned up dead in rebel uniform and have been presented by the military as guerrillas killed in combat.

The UN office in Bogota said that it had 37 cases under investigation but believed that the real number is much higher.

Colombia's armed forces are in deep crisis, amid evidence of rampant corruption and human rights abuses as the country enters its 43rd year of civil conflict.

Oxford-educated president Alvaro Uribe was re-elected last month in a landslide on the back of his security policy.

He went to Washington last week to see his closest ally, George Bush, to get a pat on the back and the promise he would continue to receive £400 million a year in aid for security.

There are politicians in the US who raised concerns, but the White House - dependent on Mr Uribe not just for the war on drugs, but to act as a counterbalance to Venezuela's left-wing leader Hugo Chavez - has ignored them.

Congressman Jim McGovern, a Democrat, tried to get Colombia's aid reduced by $30 million (£16.3 million), to pressure the Colombian president into taking action against rogue military elements, but the proposal was defeated.

Such is the loss of US influence in South America that Washington can ill-afford to alienate Colombia. Yet the fear is that the military will not be restrained by Mr Uribe, whose father was killed in a guerrilla kidnap attempt, as he seeks to crush the rebels.