Colombian investigators say two car bombs may have been used in Friday's attack on a Bogota social club which killed 33 people.

Colombia weeps but is not defeated President Alvaro Uribe

The police are being helped by agents from the US Bureau of Alcohol, Tobacco and Firearms in the search for clues.

President Alvaro Uribe has vowed to bring those responsible to justice and continue with his tough security policies.

Thousands of Colombians, shocked by the bombing, marched through the capital on Sunday to call for peace.

Speaking in a nationwide address, Mr Uribe said the security forces had determined who was behind the bombing at the multi-storey Club Nogal.

He did not name the group but other members of the government have accused the country's largest left-wing rebel group, the Revolutionary Armed Forces of Colombia (FARC).

"Colombia weeps but is not defeated, " Mr Uribe said on Sunday.

This country has suffered so much Luis Eduardo Cubillos marcher

The bomb attack, which also injured 162 people, was the biggest in Bogota in a decade and shocked city residents more used to a civil war fought in the countryside.

Earlier on Sunday, people dressed in white and from all walks of life turned out to chant "life is sacred" and call for an end to the decades-old civil war.

"Here we all are, rich and poor, agreeing that there must be peace," said Nora Vargas de Galindo, 66, as she marched with her husband, a retired lorry driver.

Child victims

Luis Eduardo Cubillos, an unemployed accountant, said no-one had the "right to kill innocent people".

The dead at the devastated club include six children.

CLUB NOGAL

Advertised as "one of the most important corporate, social and cultural centres in Bogota" Featured children's and young people's areas - they were due to close minutes before the blast Other facilities: five eating areas, art gallery, swimming-pool

With tears rolling down his face and clutching the hand of his five-year-old son, Mr Cubillos said:

"This country has suffered so much. I brought my son here to help explain the situation in Colombia but also so he sees that most Colombians are good people."

The rebels, he added, had lost sight of their original ideal of helping the Colombian people.

The BBC's Jeremy McDermott in Bogota says that despite the march against violence, the government is talking of more war, rather then peace.