The House of Representatives on Wednesday voted unanimously to honor four young Alabama girls, killed in a 1963 church bombing. Martin Luther King Jr. had called them "martyrs" of the civil rights movement.

The girls, all black members of Birmingham's 16 th Street Baptist Church, will be posthumously awarded the Congressional Gold Medal, one of the country's highest civilian honors, created by an act of Congress.

Addie Mae Collins, 14; Denise McNair, 11; Carole Robertson, 14; and Cynthia Wesley; 14, were killed on Sept 15, 1963, in the attack that struck the packed church on a Sunday morning. Twenty-two others were injured.

The bomb, composed of dynamite and a timer, was planted beneath the front steps of the church, outside a basement room in which 26 children attended a Sunday school sermon.

The blast sent a fireball into the air, blowing out a stained glass window, sending shrapnel into the air and melting metal fixtures.

Local police and fire officials searched the scene, first looking for bodies and then evidence. But at the time, few black residents of Birmingham, a hotbed of racial tension that had become so dangerous it was called "Bombingham," believed justice would be served.

At a memorial service for the girls, three days after the blast, Martin Luther King Jr., said, "These children - unoffending, innocent, and beautiful - were the victims of one of the most vicious and tragic crimes ever perpetrated against humanity."

Their deaths helped galvanize much of the country against segregation, and toward a trial of the suspects.

Witnesses reported seeing Robert Chambliss, an avowed white supremacist and member of the Ku Klux Klan. Following a short trial, less than a month after the bombing, Chambliss was found guilty of possessing dynamite and received a $100 fine. He spent six months in jail.

In 1971, Alabama Attorney General William Baxley reopened the case. Using evidence in a sealed FBI file, prosecutors charged Chambliss with murder. In 1977, he was convicted and sentenced to life in prison, where he died in 1985.

In 2000, the federal government pressed charges against three other men: Herman Cash, Thomas Blanton and Bobby Cherry, all of whom, along with Chambliss, were accused of belonging to a KKK gang called Cahaba Boys.

Cash had died by then, but in 2002, Blanton and Cherry were tried for their roles in the church bombing and found guilty of murder.

The Congressional Medal of Honor has been bestowed on other heroes of the civil rights movement, including Martin Luther King Jr., Rosa Parks and Jackie Robinson. Each medal is designed and minted specifically for its recipient.

Legislation to create the medal was co-sponsored Rep. Terri Sewell, D-Ala., and Rep. Spencer Bachus, R-Ala.