PARIS became a sea of humanity with people from all backgrounds brought together in a powerful message of unity, solidarity and defiance against the scourge of terrorism.

As far as the eye could see people clogged the French capital's boulevards, side streets and squares.

They climbed monuments and trees, they hung from lamp-posts and balconies. They carried posters, declaring Je Suis Charlie, Je Suis Flic, Je Suis Juif and Je Suis Muslim in a message of fraternity with those who had lost their lives to barbarism.

Up to 1.6 million people are believed to have marched through the streets of the French capital, with a further 2.5 million taking part in demonstrations in other cities around the country.

One thing was clear; the Unity Rally was the biggest France had ever seen.

With pride, President Francois Hollande declared: "Today, Paris is the capital of the world."

The show of solidarity came just after a video emerged showing one of the terrorists involved in the atrocities pledging his allegiance to terror group Islamic State.

Amedy Coulibaly, who killed a policewoman before murdering four hostages at a Jewish supermarket, admitted he had been working in concert with brothers Cherif and Said Kouachi, who shot dead 12 people at the Paris offices of satirical magazine Charlie Hebdo.

The men were killed by police after a long-running manhunt, with Coulibaly's wife still on the run, believed to have fled to Syria.

Despite the video, the crowd was not deterred and an unprecedented security operation was put in place to deal with the swelling numbers.

As demonstrators edged their way slowly towards the Place de la Nation, the heavy silence sometimes broke out into spontaneous cheers, applause and the national anthem as French citizens expressed their emotional defiance.

At the Place de la Republique, its monument strewn with flags and posters, chants of "Charlie, Charlie" sprang up.

The marchers carried banners, placards and posters bearing all sorts of slogans of defiance. Others carried drawings and pictures in honour of the slain cartoonists from the magazine.

A huge pencil bearing the words "not afraid" was carried through the crowd while others raised posters to create a giant image depicting the eyes and glasses of the magazine's murdered editor, Stephanie Charbonnier.

One young boy held up a poster that read: "When I grow up, I'll be a journalist. I'm not afraid."

Fanny Appelbaum, 75, who had lost two sisters and a brother in the Nazi concentration camp at Auschwitz, was defiant, saying: "We're not going to let a little gang of hoodlums run our lives. Today, we are all one."

Zakaria Moumni, a 34-year-old Franco-Moroccan draped in the French flag, added: "I am here to show the terrorists they have not won." The march, he said, was "bringing people together of all religions".

One French family said it had taken them two hours just to walk one mile. Laurent, the father, insisted: "Our values are liberty, equality and fraternity and we cannot allow terrorists to dictate to us."

Leaders from more than 40 countries, including Binyamin Netanyahu, the Israeli Prime Minister, and Mahmoud Abbas, his Palestinian counterpart, linked arms as they marched through the city in show of international unity.

David Cameron said he had taken part to "show solidarity with the French people and the French government".

Later, he said the march had been a "very moving" experience and that while it had been a "people's movement", it was right for world leaders to show unity.

"The size of the crowd was absolutely unbelievable but also the signs," said the Prime Minister. "The one I will remember the most is the one that says Je Suis Charlie, Je Suis Flic - I am police officer - et Je Suis Juif - I am a Jew.

"It is very meaningful to see people of all ages saying: 'I want to be and I am absolutely showing solidarity with those people who have suffered.'"

Matteo Renzi, the Italian Prime Minister, stressed the Unity March had offered a "moment of hope", saying: "It is beautiful, beautiful the presence of a lot of normal people, not only leaders, not only politicians."

He added: "I am absolutely convinced the people make history. In this case the people of Paris, the people of France, the people of Europe give a message for the freedom of expression, absolutely important, the attack against a rendition of journalists. We are stronger than horror and the terrorists."

Out of respect for those who had died, the world leaders walked behind the families and friends of the victims of last week's attacks.

In one moving moment, President Hollande hugged Patrick Pelloux, a doctor who is also a journalist at Charlie Hebdo. On the day of the massacre, Mr Pelloux arrived late at the magazine's office to find many of his colleagues had been murdered.

He and other survivors have vowed to publish Charlie Hebdo this week with a record print run of 1m copies. It is set to be a sell-out.

Meantime across several European cities, including Edinburgh and Glasgow, there were also marches and vigils to coincide with the one in Paris.

In London, many famous landmarks, including Tower Bridge, were lit up in the colours of the French tricolour.

In Trafalgar Square, large crowds were joined by French Ambassador Sylvie Bermann, who said: "The message is fight against terrorism to defend our voices, to defend our freedoms of opinion and expression."

ENDS