SEOUL, South Korea  In the opening months of the Korean War, the South Korean military and the police executed at least 4,900 civilians who had earlier signed up  often under force  for re-education classes meant to turn them against Communism, the country’s Truth and Reconciliation Commission announced Thursday.

The government killed the civilians out of fear that they would help the Communists who were invading from the north and forcing South Korean and American forces into retreat during the first desperate weeks of the war, the commission said.

Although the panel has reported on similar civilian massacres in the past, the announcement Thursday represented the first time that a state investigative agency confirmed the nature and scale of what is known as “the National Guidance League incident”  one of the most horrific and controversial episodes of the war.

The anti-Communist and authoritarian government of President Syngman Rhee had set up the league to re-educate people who had disavowed Communism in the months before the war, and forced an estimated 300,000 South Koreans to join. At the time, the government was facing a vicious and prolonged insurgency by leftist guerrillas.