A general view shows Hundreds of thousands of people gathering on the Place de la Republique to attend the solidarity march (Rassemblement Republicain) in the streets of Paris January 11, 2015.[Photo/Agencies]

PARIS - Dozens of world leaders gathered in Paris on Sunday to join hundreds of thousands of French citizens set to march amid high security in an unpredecented tribute to victims of this week's terrorist attacks.

Hours before the march, a video appeared online apparently made by one of the gunman before he took hostages at a Jewish supermarket on Friday, killing four before he himself was killed by police. He sat wearing white robes, a gun by his side.

Some 2,200 police and soldiers patrolled Paris streets to protect marchers from would-be attackers, with police snipers on rooftops and plain-clothes detectives mingling with the crowd. City sewers were searched ahead of the vigil and underground train stations around the march route are due to be closed down.

The silent march, starting at 3 pm (1400 GMT), reflects shock over the worst militant Islamist assault on a European city in nine years. For France, it raised questions of free speech, religion and security, and beyond French frontiers it exposed the vulnerability of states to urban attacks.

An Elysee official quoted President Francois Hollande as telling his ministers: "Paris is today the capital of the world. Our entire country will rise up and show its best side."

Seventeen people, including journalists and police, were killed in three days of violence that began with a shooting attack on the satirical newspaper Charlie Hebdo on Wednesday and ended with a hostage-taking at a Jewish deli in which four hostages were killed.

A video emerged featuring a man resembling the gunman killed in the kosher deli. He pledged allegiance to the Islamic State insurgent group and urged French Muslims to follow his example. A French anti-terrorist police source confirmed it was the killer, Amedy Coulibaly, speaking before the action.

Under a blue winter sky and bright sunshine, thousands gathered early to inspect wreaths for the victims on Place de la Republique, the square from which the march will head off through Paris later. Giant letters attached to a statue in the middle of the square spelt out "Pourquoi?" ("Why?")

Overnight, an illuminated sign on the Arc de Triomphe read: "Paris est Charlie" ("Paris is Charlie").