PARIS (AFP) - France's Prime Minister on Tuesday declared "war against terrorism", as the satirical magazine targeted in last week's Islamic extremist killing spree hit back with a defiant issue featuring the Prophet Muhammad on the cover.

A rare outpouring of national unity in the wake of the attacks that left 17 people dead spread to parliament where a packed house gave a stirring rendition of the Marseillaise anthem, a first since the end of World War I.

The special sitting came after President Francois Hollande oversaw a solemn ceremony paying tribute to three police officers killed in France's bloodiest week in decades, while four Jews shot dead in one of the attacks in Paris were laid to rest in Israel.

"Our great and beautiful France will never break, will never yield, never bend" in the face of the Islamist threat that is "still there, inside and outside" the country, said Mr Hollande, surrounded by weeping families and uniformed colleagues.

Equally defiant, the Charlie Hebdo magazine where the first attack took place on Wednesday unveiled the cover of its latest edition showing a weeping Prophet Muhammad holding a sign saying "Je suis Charlie" under the banner "All is forgiven".

"Our Muhammad is above all just a guy who is crying," said cartoonist Renald Luzier, known as Luz, who escaped the attackers' bullets as he was late for work on the day they burst into into an editorial meeting and mowed down the magazine's top staff.

"He is much nicer than the one followed by the gunmen."

Egypt's state-sponsored Islamic authority, the Dar al-Ifta, said the latest cover of Charlie Hebdo - which has been widely reproduced around the world - was "an unjustified provocation against the feelings of 1.5 billion Muslims".

But French Muslim groups urged their communities to "stay calm and avoid emotive reactions" to the depiction of Muhammad, which many see as sacrilegious.

The controversial weekly, which lampoons everyone from the pope to the president, has become the symbol of freedom of expression in the wake of the bloodshed.

This week it is preparing a print run of three million copies, compared to its usual 60,000.

ISOLATE RADICAL PRISONERS

Home to Europe's largest Jewish and Muslim communities, France was shaken to the core by the attack in which two gunmen killed 12 people in the assault on Charlie Hebdo, while a third killed a policewoman and took hostages at a Jewish supermarket where another four people died.

The supermarket killer, Amedy Coulibaly, and the Charlie Hebdo gunmen, Said and Cherif Kouachi - who were working together - were killed in quick succession in two police blitzes on Friday.

Questions have risen over how the three men, who were known to French intelligence agents and been on a US terror watch list "for years" had slipped through the cracks.

Prime Minister Manuel Valls, in a speech that drew several standing ovations, called for the intelligence capabilities and anti-terrorism laws to be strengthened after previously admitting to "clear failings" over the attackers.

"France is at war against terrorism, jihadism, radicalism. France is not at war against Islam and Muslims," Mr Valls said.

"I don't want Jews in this country to be scared, or Muslims to be ashamed" of their faith, he added.

Tackling security weaknesses, Mr Valls said convicted extremists would be isolated in prisons before the end of the year to prevent them radicalising fellow inmates.

He also said an improved system for the exchange of data on European travellers would be in place by September.

'THEY DIED FOR OUR FREEDOM'

Meanwhile, an outpouring of shock and grief that has united France and saw some four million people march across the country on Sunday, continued Tuesday as several victims were buried.

At the main police headquarters in Paris, a grim-faced Hollande laid the country's highest decoration, the Legion d'honneur, on the coffins of three fallen police officers draped in the Tricolore.

Two policemen were killed during the attack on Charlie Hebdo and a policewoman was gunned down by Coulibaly the next day when she arrived at the scene of a car accident in which he was involved. Many believe he was on his way to attack a Jewish school nearby.

"They died so that we could live in freedom," Mr Hollande said.

In Israel, thousands of mourners gathered at the funeral of the four Jews killed when Coulibaly stormed a kosher supermarket before he was himself gunned down in a dramatic police assault.

European Union counter-terrorism chief Gilles de Kerchove told AFP that jails had become "massive incubators" of radicalisation and there was no way to fully shield against such attacks.

Coulibaly, a repeat offender, met Cherif Kouachi in prison where they both fell under the spell of a renowned Islamic militant.

While the Kouachis have been linked to the Yemen-based Al-Qaeda in the Arabian Peninsula, Coulibaly claimed to have sworn allegiance to the Islamic State.

Wielding Kalashnikovs and a rocket launcher, the brothers were cornered by police on Friday after a massive manhunt following their attack on Charlie Hebdo.

Elite security forces gunned them down after they ran out of a printworks where they had holed up, spraying bullets in a final act of defiance.

To ease fears in a nation still jittery after its worst attacks in half a century, Defence Minister Jean-Yves Le Drian announced that some 10,000 troops will be deployed to protect sensitive sites.

France has been on high alert for several months over its citizens who go to fight alongside Islamic State jihadists in Iraq and Syria, some of whom have been pictured in grisly execution videos.

The head of European police agency Europol, Rob Wainwright, said up to 5,000 European Union citizens have joined Islamic militant ranks.

Mr Valls also said 1,400 people were known to have left France to fight in Syria and Iraq, or were planning to do so. Seventy French citizens have died there.