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 American 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 American forces in Korea, and the first evidence that that policy was known to upper ranks of the American government.

“If refugees do appear from north of U.S. lines they will receive warning shots, and if they then persist in advancing they will be shot,” wrote Ambas sador John Muccio, in his message to the 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, American commanders repeatedly ordered refugees shot, documents show.