Cassie Sadusky, 25, left, and her sister Jetta, 22, visit the gravesites of Columbine students Corey DePooter and Rachel Scott at Chapel Hill Memorial Gardens near Littleton, Colo., on Monday. (Ed Andrieski/Associated Press)

U.S. talk show host Oprah Winfrey cancelled Monday's taped show marking the 10th anniversary of the Columbine High School shootings, saying she felt it focused too much on the shooters rather than the victims.

"I decided to pull the Columbine show today. After reviewing it, I thought it focused too much on the killers. Today, hold a thought for the Columbine community. This is a hard day for them," Winfrey wrote on Oprah.com and her Facebook page.

Winfrey's action came amid muted commemorations of the massacre in the Denver, Colo., suburb of Littleton that claimed the lives of 12 students and a teacher. Another 26 people were wounded.

On the morning of April 20, 1999, two Columbine seniors — Eric Harris, 18, and Dylan Klebold, 17 — unleashed an attack on their schoolmates with guns and pipe bombs before killing themselves.

To mark the anniversary, flags flew at half-mast over the Colorado Capitol and other government buildings. State legislators passed a resolution titled "Triumph Over Tragedy."

About 50 demonstrators gathered at the Capitol for a "lie-in" in support of gun control. Thirteen people representing those who were killed lay on the lawn with blue and white ribbons wrapped around their necks, the colours of the school.

At the event was Tom Mauser, father of Daniel Mauser, who was killed at Columbine.

"[The gunmen] did not kill their spirits," Mauser said of the victims. "They did not kill our spirits either."

A moment of silence and the tolling of bells marked each of 13 names that were read.

A memorial service was planned for Monday night in Clement Park, which is next to the high school.

With files from The Associated Press