Paris (AFP) - France announced an unprecedented deployment of thousands of troops and police to bolster security at "sensitive" sites including Jewish schools Monday, a day after marches gathering nearly four million people countrywide.

"We have decided ... to mobilise 10,000 men to protect sensitive sites in the whole country from tomorrow (Tuesday) evening," Defence Minister Jean-Yves Le Drian said after an emergency security meeting.

"This is the first time that our troops have been mobilised to such an extent on our own soil," he added.

Prime Minister Manuel Valls said one of the Islamists responsible for last week's attacks that rocked France -- Amedy Coulibaly who gunned down a policewoman and four Jewish shoppers at a kosher supermarket -- likely received help from others.

"We think there are in fact probably accomplices," Valls told French radio. "The hunt will go on."

A hostage from the Jewish supermarket described the harrowing events to Europe 1 radio on Monday.

"When I arrived in the entrance of the store ... I saw a body, seated on the floor with its head leaning. I felt like I was in a bad movie," the woman said.

The alert level in shell-shocked France remained at its highest possible as the interior minister announced the deployment of nearly 5,000 police to guard Jewish schools and places of worship.

Bernard Cazeneuve said he was putting in place a "powerful and durable" system of protection for France's Jewish community, the largest in Europe.

Israeli Prime Minister Benjamin Netanyahu visited the scene of the hostage drama at the kosher supermarket in eastern Paris on Friday.

To cries of "Bibi, Bibi" -- his nickname -- and under extensive security protection, Netanyahu paid tribute to the four Jewish men who died at the store.

They will be buried in Israel on Tuesday.

Netanyahu, who joined Hollande at the main synagogue in Paris after Sunday's march, had praised the "very firm position" taken by French leaders against what he called "the new anti-Semitism and terrorism" reigning in France.

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Muslims are also coming under attack, with community leaders reporting more than 50 incidents recorded since the assault on the Charlie Hebdo satirical magazine, including apparent arson at a mosque in Poitiers on Sunday.

That came after more than 1.5 million people marched through Paris in solidarity and sorrow in the biggest rally in modern French history.

In an extraordinary show of unity, dozens of world leaders, including from Israel and the Palestinian Authority, linked arms at the front of the march led by victims' families.

During an emotional and colourful rally, the crowd brandished banners saying, "I'm French and I'm not scared."

In tribute to the cartoonists slaughtered at Charlie Hebdo, marchers also held up signs saying: "Make fun, not war" and "Ink should flow, not blood".

President Francois Hollande proclaimed Paris the "capital of the world", while millions turned out in other French cities and around the world.

Pope Francis responded to the week's bloody events on Monday, blaming the breakdown of society and the way people "become enslaved, whether to the latest fads, or to power, money, or even deviant forms of religion."

- 'New anti-Semitism' -

Hollande has warned his grieving countrymen not to let down their guard and questions were mounting as to how the attackers slipped through the intelligence services' net.

As well as Coulibaly, brothers Said and Cherif Kouachi, who carried out the Charlie Hebdo murders in what they said was revenge for the magazine's lampooning of the Prophet Mohammed, had a history of extremism and were known to French intelligence.

Valls has admitted there were "clear failings" after it emerged that the Kouachis had been on a US terror watch list "for years".

He told French radio on Monday he wanted to see an "improved" system of tapping phones.

Valls also said 1,400 people were known to have left to fight in Syria and Iraq, or were planning to do so, up from the 1,200 stated last month. Seventy French citizens have died there.

Said Kouachi, 34, was known to have travelled to Yemen in 2011, where he received weapons training from Al-Qaeda in the Arabian Peninsula. And 32-year-old Cherif was a known jihadist convicted in 2008 for involvement in a network sending fighters from France to Iraq.

Coulibaly was a repeat criminal offender also convicted for extremist activity.

All three were shot dead by police Friday after a three-day reign of terror that culminated in twin hostage dramas.

Investigators have been trying to hunt down Coulibaly's partner, 26-year-old Hayat Boumeddiene, but a security source in Turkey told AFP she arrived there on January 2, before the attacks, and has probably travelled on to Syria.

Coulibaly's mother and sisters condemned his actions, saying "we hope there will not be any confusion between these odious acts and the Muslim religion".