DUISBURG, Germany - Germany held a memorial service Saturday for the victims of the Love Parade techno music festival, where 21 people were crushed to death and 500 injured in a tunnel that was the only entrance to the event.

The memorial at Salvator Church, which opened with sombre organ music, was shown on screens in a football stadium and a dozen other churches in the western city of Duisburg. Several TV stations carried the service live, and flags across the country flew at half-mast.

Chancellor Angela Merkel and President Christian Wulff were at the event. Family members of the victims also attended.

The 21 people who died were aged 18 to 38 and included foreigners from Spain, Australia, Italy, Bosnia, China and Holland.

The ceremony was led by Roman Catholic and Lutheran Protestant clerics -- representing Germany's two main denominations.

"The Love Parade was danced to death," Nikolaus Schneider, the head of the Rhineland Lutheran church assembly, said in his sermon. "In the middle of a celebration of lust for life, death showed its ugly face to all of us."

Franz-Josef Overbeck, the Catholic bishop of the neighbouring city of Essen, said: "Life can be so oppositional: One moment there is a party, the next moment we are lying helplessly on the ground."

"We want to stir our life in secure ways, but don't have it under control."

After the sermons, rescue helpers lit 21 candles for the victims of the tragedy.

Anger had been building in recent days, with over 250 people protesting in Duisburg on Thursday and demanding the resignation of the city's mayor, Adolf Sauerland.

People blame Sauerland and the city's authorities for failing to adequately plan for the event. Private organizers also have come under fire for allegedly trying to squeeze as many as 1.4 million revelers into too small a space and for allowing only one access point onto the festival grounds.

A preliminary report by police investigators Wednesday accused the organizer of the Love Parade of major security breaches which may have led to the crush. But it left many unanswered questions regarding the responsibility of the Duisburg municipality, which was to oversee the event.

The crush occurred in the jam-packed tunnel that was the sole entrance point to the festival grounds.

Since the tragedy, hundreds of people have lit candles, left notes and placed flowers on the site of the deaths and injuries.