Correspondent Ruth Morris: "The most significant civil action in Colombian history"

Some two million people marched in the capital city of Bogota, while nearly a million more took the streets of Medellin.

Protesters waved Colombian flags and small paper flags bearing the simple slogan "No Mas".

The anti-war protest took place as long-awaited peace negotiations began in a rebel-held southern town.

A Colombian waves a small 'No Mas' flag in front of a banner

Marchers in 15 cities and dozens of towns turned out to demand a ceasefire, swift progress in peace talks and an end to violence against civilians - the principal victims in the war that has left more than 120,000 dead since 1964.

"We're fed up with all this violence. ... we want all the men of violence to cease armed actions against unarmed citizens," said Francisco Santos, one of the main organisers of the demonstrations.

Social worker Matilde Abril said she had to flee Casanare province because guerrillas, right-wing militias and common criminals had made life there too dangerous.

"We don't even go back there anymore ... not even on vacation."

Peace talks began

As protesters took to the streets, government and guerrilla negotiators from the Revolutionary Armed Forces (FARC) convened in Uribe - a small mountain town in the heart of the demilitarised zone - for their first talks since mid-July.

A FARC rebel guards the village where the peace talks are being held

The FARC, which has some 17,000 fighters nationwide, broke off talks in protest at President Andres Pastrana's demands that international monitors oversee talks.

While both sides boast that peace prospects are more promising than ever, they are also cautioning strongly against expectations of a quick resolution to the conflict.

Many Colombians are hoping the antiwar movement - unparalleled in the South American nation where peace activists have been systematically killed by extremists - will light a fire under the negotiators' feet.

Escalating violence

The protests come amid an escalation in violence that dampened much of the optimism generated by recent moves to forge peace.

Many Colombians were jolted out of apathy by a surge this year in guerrilla ransom kidnappings and the August assassination of comic and peace advocate Jaime Garzon.

Not all Colombians were moved.

"To end the violence, you need jobs and education. You can't change everything with a march," said car-wash employee Henry Pineda, working as the marchers passed by.