Orders for U.S. troops to fire on civilians during the Korean War were illegal, and the men who followed them at No Gun Ri could have faced court-martial, legal specialists say.

"It's pretty simple: Soldiers are not allowed to shoot noncombatants," said Gary D. Solis, who teaches the law of war at the U.S. Military Academy at West Point.But prosecuting the gray-haired veterans today is a practical impossibility, experts say. And at the time in Korea, they say, such events apparently were ignored by officers up the chain of Army command.

"I can't understand why I didn't know about it. I guess because it was kept quiet," Howard Levie, who was a top Army war crimes prosecutor in 1950, said of the No Gun Ri killings.

The Associated Press reported Wednesday that a dozen veterans of the 1st Cavalry Division, corroborating the accounts of survivors, said their unit killed a large number of South Korean refugees at No Gun Ri, a hamlet 100 miles southeast of the South Korean capital of Seoul.

The survivors say 400 people were killed in the mass shooting and a preceding U.S. air attack.

The ex-soldiers say they shot the civilians, because they feared disguised North Korean soldiers were among the group. Some veterans said they received sporadic gunfire from among the refugees. Others do not remember hostile fire.

The fear of enemy infiltrators led U.S. commanders in the early days of the Korean War to issue orders to fire on refugees, according to declassified documents found by the AP in the National Archives in Washington.

The 25th Infantry Division commander instructed his troops that civilians in the battle zone "are to be considered as enemy and action taken accordingly." In the 1st Cavalry Division, the operations chief issued this order: "No refugees to cross the front line. Fire everyone trying to cross lines. Use discretion in case of women and children."

Such orders are patently illegal, military law experts say.

"I have never heard of orders like this, not outside the orders given by Germans that we heard about during the Nuremberg Trials," said Scott Silliman of Duke University, a retired colonel and Air Force lawyer for 25 years.

During the 1950-53 war, there were no prosecutions of anything more than individual murders of civilians by U.S. servicemen, the experts note.

For one thing, the Army's cadre of lawyers, the Judge Advocate Generals Corps, "was relatively small when the Korean War broke out," said Joseph Kelly, a retired colonel who was a Pentagon lawyer during the Korean conflict.

"It's now larger and permeates the structure more, and the officers tend to rely on them to keep out of trouble," said Kelly, a professor of international law.