Dozens of world leaders including Muslim representatives will join hundreds of thousands of French citizens to march amid high security through Paris on Sunday in an unpredecented tribute to victims of this week's Islamist militant attacks.

Some 2,200 security personnel were being drafted in 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 p.m. (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.

Seventeen people, including journalists and policemen, lost their lives 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 kosher supermarket on Friday. The three gunmen were also killed.

"It will be an unprecedented demonstration that will be written in the history books," Prime Minister Manuel Valls said. "It must show the power and dignity of the French people, who will cry out their love of liberty and tolerance."

German Chancellor Angela Merkel, British Prime Minister David Cameron and Italy Prime Minister Matteo Renzi will be among over 40 foreign leaders marching with President Francois Hollande. Turkish Prime Minister Ahmet Davutoglu and Israel's Benjamin Netanyahu - who earlier encouraged French Jews to emigrate to Israel - are also expected to take part.

Turkish and French sources said that a woman hunted by French police as a suspect in the attacks had left France several days before the killings and is believed to be in Syria.

EUROPE'S BIGGEST MUSLIM MINORITY

French police had launched in an intensive search for Hayat Boumeddiene, the 26-year-old partner of one of the attackers, describing her as "armed and dangerous".

But a source familiar with the situation said Boumeddiene left France last week and travelled to Syria via Turkey. A senior Turkish official corroborated that account, saying she passed through Istanbul on Jan. 2.

A senior Turkish security official said Paris and Ankara were now cooperating in trying to trace her but that she had arrived in Istanbul without any warning from France.

"We think she is in Syria at the moment but we do not have any evidence about that. She is most probably not in Turkey," the Turkish source said.

Twelve people were killed in Wednesday's initial attack on Charlie Hebdo, a journal know for satirising religions and politicians, including its top cartoonists. The attackers singled out the weekly newspaper for its publication of cartoons depicting and ridiculing the Prophet Mohammad.

Under a blue winter sky and bright sunshine, a few hundred people gathered early to look at 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?")

"I am here to show the terrorists they have not won - on the contrary, it is bringing people together of all religions," said Zakaria Moumni, a 34-year-old Franco-Moroccan draped in the French flag.

Across France on Saturday, hundreds of thousands of people took part in rallies to demonstrate against the attacks. Many people carried signs saying "Je suis Charlie" (I am Charlie).

"I want my child to be born in a better world," Pierine, 29 and heavily pregnant, said at a march in the Mediterranean city of Nice.

On Sunday, public transport in the Paris region was to be free. In a huge security operation, plainclothes policemen were to protect leading personalities, with snipers posted on rooftops along the route from Place de la Republique to Place de la Nation.

"Everything will be done to make sure that those who want to come to this meeting can do so safely," Interior Minister Bernard Cazeneuve said.

However, right-wing National Front leader Marine Le Pen, who is expected to receive a boost in the polls due to the attacks, said her party would shun the Paris demonstration and instead take part in regional marches.

The Front's support hinges to a great extent on France's difficulties in integrating its five-million Muslim population, the biggest in Europe.

Le Pen accused the Socialist government of trying to take advantage of the event to win greater support.

"This afternoon, Paris will be the world capital of resistance against terrorism and of the defence of freedom, it will really be the world march for freedom," French Foreign Minister Laurent Fabius said on television on Sunday.

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