PARIS, Jan. 11-- Millions in Paris and elsewhere walked in solemn processions on Sunday to denounce terrorism that has inflicted a deep scar on France in a three-day bloodshed that claimed 17 victims.

Demonstrators holding various national flags or banners filled boulevards across Paris as they followed over 40 world leaders who marched arm-in-arm at the front of an unusual massive gathering in the wake of a spree of terror attacks that has shocked and angered beyond the French border.

Local reports said Sunday's rally was the largest in Paris since its liberation from Nazi Germany in 1944.

France was plunged into grief and indignation after gunmen killed 17 people in separate attacks over three days in Paris, with 12 killed at the headquarters of the satirical magazine Charlie Hebdo and four at a kosher supermarket.

Political dignitaries leading Sunday's unity rally in Paris were mainly heads of state or government in Europe. Other prominent participants included Israeli Prime Minister Benjamin Netanyahu and Palestinian President Mahmoud Abbas.

Demonstrators also staged mass rallies to show solidary with France at landmarks in London, Berlin, Madrid, Vienna, in the Middle East and on the other side of the Atlantic.

Thousands of people, with many holding placards, pencils, French flags and portraits of the victims, gathered at Trafalgar Square in London for a unity rally at the same time when a massive march took place in Paris.

British Deputy Prime Minister Nick Clegg and French ambassador to Britain Sylvie Bermann also joined the crowds at Trafalgar Square, where a vigil was held in tribute to the victims.

The city also lit up its landmarks in colors of the French national flag late Sunday to show solidarity.

While in Vienna, some 12,000 people gathered for the same purpose. Before the rally at Ballhausplatz, hundreds had shown up with flowers and candles at the French embassy in Vienna.

In the Middle East cities of Cairo and Jerusalem, people also gathered to pay tributes to victims of the Paris attacks.

Across the Atlantic, about 25,000 people marched in Canada's French-speaking city of Montreal.

In the U.S. capital, thousands of people joined a silent march led by French ambassador Gerard Araud.

Though all the three gunmen behind the Paris attacks were killed by police, France has maintained a high security level and many other countries upgraded their terror alert level in response to the attacks.