On Dec. 29, 1890, along Wounded Knee Creek on the Pine Ridge Reservation in southwestern South Dakota, the U.S. Army killed hundreds of unarmed members of the Lakota Sioux tribe, including many women and children.

In the aftermath of one of the bloodiest acts of violence against Native Americans by federal forces, the government looked into the conduct of the troops of the 7th Cavalry and decided to award 20 Medals of Honor, the nation's highest military commendation, to soldiers involved in the massacre.

Now members of the tribe are stepping up a long-running pressure campaign to have the medals rescinded, saying that the government should recognize the atrocity for what it was and help heal the historical wounds of that day.

They recently won support from the state Senate in South Dakota, which passed a resolution in February urging Congress to investigate the award of the medals. On Capitol Hill, proponents of the effort, led by Sens. Elizabeth Warren of Massachusetts and Jeff Merkley of Oregon, both Democrats, are hoping to make a new push on behalf of legislation they have sponsored, the "Remove the Stain" bill, that would rescind the medals.

"I believe on our reservation, we have a pervasive sadness that exists here because of what happened at Wounded Knee, the massacre, and it has never been resolved, and there has never been closure," said Marcella Lebeau, a citizen of the Two Kettle Band, Cheyenne River Sioux. Lebeau, a 101-year-old veteran who served during World War II as a surgical nurse near the front at the 25th General Hospital in Liège, Belgium, and later worked for the Indian Health Service, is among those pushing for the medals to be rescinded.

Many of the award citations noted "gallant conduct in battle" and "distinguished" or "conspicuous" bravery, while documenting few details to justify those characterizations.

To date, the nation has awarded more than 3,500 Medals of Honor, including about 400 to soldiers who fought during campaigns against American Indians. About 900 awards have been rescinded, according to the Congressional Medal of Honor Society, most for awards made during the Civil War, but no medals awarded for service in the Indian campaigns have been revoked.