More than a half-century after hostilities ended in Korea, a document from the war's chaotic early days has come to light — a letter from the U.S. ambassador to Seoul, informing the State Department that American soldiers would shoot refugees approaching their lines.

The letter — dated the day of the Army's mass killing of South Korean refugees at No Gun Ri in 1950 — is the strongest indication yet that such a policy existed for all U.S. forces in Korea, and the first evidence that that policy was known to upper ranks of the U.S. government.

"If refugees do appear from north of US lines they will receive warning shots, and if they then persist in advancing they will be shot," wrote Ambassador John J. Muccio, in his message to Assistant Secretary of State Dean Rusk.

The letter reported on decisions made at a high-level meeting in
South Korea on July 25, 1950, the night before the 7th U.S. Cavalry Regiment shot the refugees at No Gun Ri.

Estimates vary on the number of dead at No Gun Ri. American soldiers' estimates ranged from under 100 to "hundreds" dead; Korean survivors say about 400, mostly women and children, were killed at the village 100 miles southeast of Seoul, the South Korean capital. Hundreds more refugees were killed in later, similar episodes, survivors say.

The No Gun Ri killings were documented in a Pulitzer Prize-winning story by The Associated Press in 1999, which prompted a 16-month
Pentagon inquiry.

The Pentagon concluded that the No Gun Ri shootings, which lasted three days, were "an unfortunate tragedy" — "not a deliberate killing." It suggested panicky soldiers, acting without orders, opened fire because they feared that an approaching line of families, baggage and farm animals concealed enemy troops.

But Muccio's letter indicates the actions of the 7th Cavalry were consistent with policy, adopted because of concern that North Koreans would infiltrate via refugee columns. And in subsequent months, U.S. commanders repeatedly ordered refugees shot, documents show.

The Muccio letter, declassified in 1982, is discussed in a new book by American historian Sahr Conway-Lanz, who discovered the document at the U.S. National Archives, where the AP also has obtained a copy.

Conway-Lanz, a former Harvard historian and now an archivist of the National Archives' Nixon collection, was awarded the Stuart L. Bernath Award of the Society for Historians of American Foreign Relations for the article on which the book is based.

"With this additional piece of evidence, the Pentagon report's interpretation (of No Gun Ri) becomes difficult to sustain," Conway-Lanz argues in his book, "Collateral Damage," published this spring by Routledge.

The Army report's own list of sources for the 1999-2001 investigation shows its researchers reviewed the microfilm containing the Muccio letter. But the 300-page report did not mention it.

Asked about this, Pentagon spokeswoman Betsy Weiner would say only that the Army inspector general's report was "an accurate and objective portrayal of the available facts based on 13 months of work."

Said Louis Caldera, who was Army secretary in 2001 and is now University of New Mexico president, "Millions of pages of files were reviewed and it is certainly possible they may have simply missed it."

Ex-journalist Don Oberdorfer, a historian of Korea who served on a team of outside experts who reviewed the investigation, said he did not recall seeing the Muccio message. "I don't know why, since the military claimed to have combed all records from any source."

Muccio noted in his 1950 letter that U.S. commanders feared disguised North Korean soldiers were infiltrating American lines via refugee columns.

As a result, those meeting on the night of July 25, 1950 — top staff officers of the U.S. 8th Army, Muccio's representative Harold J. Noble and South Korean officials — decided on a policy of air-dropping leaflets telling South Korean civilians not to head south toward U.S. defense lines, and of shooting them if they did approach U.S. lines despite warning shots, the ambassador wrote to Rusk.

Rusk, Muccio and Noble, who was embassy first secretary, are all dead. It is not known what action, if any, Rusk and others in Washington may have taken as a result of the letter.

Muccio told Rusk, who later served as U.S. secretary of state during the Vietnam War, that he was writing him "in view of the possibility of repercussions in the United States" from such deadly U.S. tactics.

But the No Gun Ri killings — as well as others in the ensuing months — remained hidden from history until the AP report of 1999, in which ex-soldiers who were at No Gun Ri corroborated the Korean survivors' accounts.

Survivors said U.S. soldiers first forced them from nearby villages on July 25, 1950, and then stopped them in front of U.S. lines the next day, when they were attacked without warning by aircraft as hundreds sat atop a railroad embankment. Troops of the 7th Cavalry followed with ground fire as survivors took shelter under a railroad bridge.

The late Army Col. Robert M. Carroll, a lieutenant at No Gun Ri, said he remembered the order radioed across the warfront on the morning of July 26 to stop refugees from crossing battle lines. "What do you do when you're told nobody comes through?" he said in a 1998 interview. "We had to shoot them to hold them back."

Other soldier witnesses attested to radioed orders to open fire at No Gun Ri.

Since that episode was confirmed in 1999, South Koreans have lodged complaints with the Seoul government about more than 60 other alleged large-scale killings of refugees by the U.S. military in the 1950-53 war.

The Army report of 2001 acknowledged investigators learned of other, unspecified civilian killings, but said these would not be investigated.

Meanwhile, AP research uncovered at least 19 declassified U.S. military documents showing commanders ordered or authorized such killings in 1950-51.