Hundreds of thousands of Colombians have poured onto the streets of Bogota to protest against Marxist Farc rebels.
Colombians in Cali demonstrate against the Farc
The protesters waved flags and wore T-shirts with the slogan: "No more kidnapping, no more lies, no more deaths, no more Farc."
Some estimates put the number of people protesting in Bogota at between 500,000 and two million.
Thousands more protested elsewhere in Colombia, and in close to 100 other cities around the world.
Colombian president Alvaro Uribe told people in the north-eastern town of Valledupar: "To our fellow countrymen who live abroad, and who today have united with the rest of their compatriots, we extend our gratitude."
On the streets of Bogota, the message was blunter.
"No more Farc, we don't want any more Farc, young people have to say no to the Farc and tell them to stop their violence," student Jaime Martinez said.
Former hostage Clara Rojas, who was freed last month after nearly six years as a captive, said: "I hope the Farc is listening."
And a woman marching with her three children told the BBC: "I think this march will set a precedent in Colombia because for the first time all Colombians are going to protest as one body."
Schools were closed in many big cities, and businesses closed, allowing workers to march.
The protest was started less than a month ago on the social networking website Facebook by a 33-year-old engineer, Oscar Morales, from his home in Barranquilla on Colombia's Caribbean coast.
Over 250,000 Facebook users signed on, and the movement was taken up by newspapers and radio and television stations across the country.
Some people, including relatives of kidnap victims, oppose it.
Paris was one of the cities hosting an anti-Farc demonstration
They fear the demonstrations may provoke Farc into treating more harshly the 700 captives it is believed to be holding. It has been fighting the Colombian government for 44 years.
"Maybe neither the hostages nor the humanitarian exchange or peace will benefit," the mother of Ingrid Betancourt, a high-profile hostage, is quoted as saying in Semana magazine.
But armed forces chief Gen Freddy Padilla says negative coverage coming from the 'No More' movement was behind the Farc's weekend announcement that it would release three more political captives.
The rebels said that former lawmakers Luis Eladio Perez, Gloria Polanco and Orlando Beltran, who have been held for over six years, were to be released on the grounds of their health.
No further details were given.
But letters from fellow captives, carried by freed hostages Clara Rojas and Consuelo Gonzales last month, describe harsh detention conditions and debilitating jungle illnesses including malaria and chronic diarrhoea.
A Farc statement said that the planned release sprang from mediation efforts by Venezuelan President Hugo Chavez in the long-running conflict.
The role of Mr Chavez has caused diplomatic tensions
The group offered to make the handover to Mr Chavez and a Colombian opposition senator "personally, or through representatives".
The group released Ms Rojas and Ms Gonzales in January in a deal that Mr Chavez helped to broker.
The BBC's Jeremy McDermott, reporting from Bogota, says the march has showed two things: the deep vein of outrage among ordinary Colombians over the Farc's violence; and the power of the internet to mobilise people across the world.
But he says it remains to be seen whether the Farc, which has traditionally been impervious to public opinion, will listen to the voices raised against it.