The demonstrators were both remembering the victims of what they say was a brutal era and urging the government to press ahead with extradition.

They laid 3,197 white carnations outside the building in London and made them into a tapestry on metal railings - each flower representing someone who died or disappeared during General Pinochet's era.

The protesters' caricature of General Pinochet

The flowers, which symbolise death in Chile, were placed as the protesters also marked the 50th anniversary of the Universal Declaration of Human Rights.

The demonstration was sponsored by human rights group Amnesty International and was originally planned to encourage Home Secretary Jack Straw to allow the former dictator's extradition to Spain.

But following his decision to allow extradition proceedings to go ahead, it became a ceremony of remembrance as well as a reminder by Amnesty to the government to ensure legal proceedings run their course.

Princess backs service

Many protesters wore black, with white face masks, and carried placards showing faces of disappeared relatives or friends, with, written above in Spanish, the question, Where is he or she?

One masked placard bearer, Pedro Affendano, said a number of his friends had died following Pinochet's coup.

He said that while the extradition proceedings might cause internal friction, he felt it was a process worth going through.

"I think it will be difficult but healthy for the country. There have been too many questions, now we need some answers," he said.

The Princess Royal arriving for the service at Wesminster Abbey

Many of the demonstrators had attended an Amnesty International inter-faith service at Westminster Abbey, at which the Princess Royal was guest of honour.

It had been originally planned to highlight the objectives of the human rights declaration over the past 50 years.

The Spanish judge seeking General Pinochet's extradition has formally charged him with crimes against humanity.

The general is due to appear before Belmarsh magistrates in London on Friday.

The decision over his future has deeply divided politicians in the UK, with Labour MPs saying he must face charges of genocide but Conservatives arguing it would be wrong to interfere with another country's justice system.