Media playback is unsupported on your device Media caption Samantha Haviland was a student at Columbine High School when the 1999 shooting happened

Survivors of the Columbine High School shooting have been speaking at a remembrance ceremony in Denver to mark the twentieth anniversary of the massacre.

Twelve students and a teacher were murdered by two teenagers.

A former student, Patrick Ireland, who was injured by bullets, said no one from the school or surrounding community had emerged unscathed.

The event was the culmination of three days of commemorations. Earlier, members of the public left flowers and cards at a memorial to the victims.

Media playback is unsupported on your device Media caption Bill Clinton spoke at the remembrance ceremony via video link

Columbine students and staff also marked the day by taking part in community service projects.

Image copyright Getty Images Image caption Survivor Will Beck placed flowers at the Columbine Memorial at Clement Park in Littleton, Colorado

Image copyright Getty Images Image caption Sean Graves, a massacre survivor and 2002 graduate, spoke during the ceremony

Image copyright Getty Images Image caption Crosses with the names and portraits of the victims at Chapel Hill Memorial Gardens, also in Littleton, Colorado

Image copyright Getty Images Image caption People gathered to remember loved ones at the Columbine Memorial

Image copyright Getty Images Image caption Spencer Greenlee, a student at Columbine High School, sat in prayer at the memorial

Image copyright Getty Images Image caption Candles around a collection of flowers laid at the memorial