Here's a Newsweek article, "The Salvador Option" from January 14, 2005:
...Now, NEWSWEEK has learned, the Pentagon is intensively debating an option that dates back to a still-secret strategy in the Reagan administration’s battle against the leftist guerrilla insurgency in El Salvador in the early 1980s. Then, faced with a losing war against Salvadoran rebels, the U.S. government funded or supported "nationalist" forces that allegedly included so-called death squads directed to hunt down and kill rebel leaders and sympathizers. Eventually the insurgency was quelled, and many U.S. conservatives consider the policy to have been a success—despite the deaths of innocent civilians and the subsequent Iran-Contra arms-for-hostages scandal. (Among the current administration officials who dealt with Central America back then is John Negroponte, who is today the U.S. ambassador to Iraq. Under Reagan, he was ambassador to Honduras. There is no evidence, however, that Negroponte knew anything about the Salvadoran death squads or the Iran-Contra scandal at the time. The Iraq ambassador, in a phone call to NEWSWEEK on Jan. 10, said he was not involved in military strategy in Iraq. He called the insertion of his name into this report "utterly gratuitous.")Link
Following that model, one Pentagon proposal would send Special Forces teams to advise, support and possibly train Iraqi squads, most likely hand-picked Kurdish Peshmerga fighters and Shiite militiamen, to target Sunni insurgents and their sympathizers, even across the border into Syria, according to military insiders familiar with the discussions. It remains unclear, however, whether this would be a policy of assassination or so-called "snatch" operations, in which the targets are sent to secret facilities for interrogation. The current thinking is that while U.S. Special Forces would lead operations in, say, Syria, activities inside Iraq itself would be carried out by Iraqi paramilitaries, officials tell NEWSWEEK. ...
Here's an article from the Covert Action Quartly, Summer 1990: "Death Squads in El Salvador: A Pattern of U.S. Complicity"
In 1963, the U.S. government sent 10 Special Forces personnel to El Salvador to help General Jose Alberto Medrano set up the Organizacion Democratica Nacionalista (ORDEN)-the first paramilitary death squad in that country. These Green Berets assisted in the organization and indoctrination of rural "civic" squads which gathered intelligence and carried out political assassinations in coordination with the Salvadoran military.
Now, there is compelling evidence to show that for over 30 years, members of the U.S. military and the CIA have helped organize, train, and fund death squad activity in El Salvador.
In the last eight years, six Salvadoran military deserters have publicly acknowledged their participation in the death squads. Their stories are notable because they not only confirm suspicions that the death squads are made up of members of the Salvadoran military, but also because each one implicates U.S. personnel in death squad activity. ...
From the final paragraphs:
...Carlos Antonio Gomez Montano was a paratrooper stationed at Ilopango Air Force Base. He claimed to have seen eight Green Beret advisers watching two "torture classes" during which a 17-year-old boy and a 13-year-old girl were tortured. Montano claimed that his unit and the Green Berets were joined by Salvadoran Air Force Commander Rafael Bustillo and other Salvadoran officers during these two sessions in January 1981. A Salvadoran officer told the assembled soldiers, "[watching] will make you feel more like a man.''Link
Above are the accounts of the death squad deserters. Non military sources have also reported the participation of U.S. personnel. For example, another (highly placed anonymous civilian) source maintained that Armed Forces General Staff Departments 2 and 5 (organized with help from U.S. Army Colonel David Rodriguez, a Cuban-American) used tortures such as beating, burning and electric shock. U.S. involvement has also been asserted in sworn accounts by some victims of torture. Jose Ruben Carrillo Cubas, a student, gave testimony that during his detention by the Long Distance Reconnaissance Patrol (PRAL) in 1986, a U.S. Army Major tortured him by applying electric shocks to his back and ears.
Various sources have reported the use of U.S.-manufactured torture equipment. Rene Hurtado, for example, explained, "There re some very sophisticated methods...of torture..[like the machine] that looks like a radio, like a transformer; it s about 15 centimeters across, with connecting wires. It says General Electric on it...."
Many other documented accounts of brutality by U.S. trained and advised military units exist. Indeed, the elite Atlacatl Battalion has been implicated in several massacres over the past ten years and members of the battalion have been indicted for the November slayings of the six Jesuit priests and two women.
It is widely accepted, in the mainstream media and among human rights organizations, that the Salvadoran government is responsible for most of the 70,000 deaths which are the result of ten years of civil war. The debate, however, has dwelled on whether the death squads are strictly renegade military factions or a part of the larger apparatus. The evidence indicates that the death squads are simply components of the Salvadoran military. And that their activities are not only common knowledge to U.S. agencies, but that U.S. personnel have been integral in organizing these units and continue to support their dally functioning.