French President Francois Hollande on Tuesday honoured the victims of the jihadist rampage a year ago in Paris that began with an assault on satirical weekly Charlie Hebdo, but the widow of a slain police bodyguard said she was taking legal action over alleged security failings.

Hollande began the commemorations by inaugurating a plaque at Charlie Hebdo's former offices, where cartoonists who were household names in France, nicknamed Cabu, Wolinski and Charb, were killed along with nine others by radicalised brothers Said and Cherif Kouachi.

But Ingrid Brinsolaro, the widow of Charb's bodyguard Franck Brinsolaro who was killed alongside him in the attack on January 7, 2015, said she had filed a lawsuit claiming that her husband was left vulnerable because Charlie Hebdo was inadequately protected.

"To me, Franck was sacrificed, there's no other word for it. He saw shortcomings, he regretted the lack of security at the offices. He said it was a 'sieve' and it was impossible to do his job right in those conditions," she said on French television Tuesday.

In the two days after the attack on Charlie Hebdo, a policewoman and four Jews at a kosher supermarket were shot dead by another jihadist, Amedy Coulibaly.

Dubbed "France's 9/11", the attacks marked the start of a string of jihadist strikes in France that culminated in the November 13 attacks in Paris that left 130 dead.

The massacre at Charlie Hebdo unleashed an outpouring of solidarity for freedom of expression, with the rallying cry "Je Suis Charlie" taken up around the world.

After Tuesday's sombre ceremony, Hollande could be seen embracing cartoonist Georges Wolinski's widow Maryse.

Red-faced authorities admitted later that they had misspelled Wolinski's name on the plaque, and rapidly corrected the error.

The president and Paris Mayor Anne Hidalgo unveiled a separate plaque nearby at the site where one of the gunmen shot police officer Ahmed Merabet as he lay on the pavement.

They went on to unveil a third plaque at Hyper Cacher, the kosher store in an eastern suburb where three shoppers and an employee were killed during a horrifying hostage drama.

Hollande greeted Lassana Bathily, the Muslim worker at the supermarket credited with saving many shoppers' lives by helping them hide in an underground cold room and later helping police to mount the raid in which they killed Coulibaly.

Bathily, a Malian who was given French nationality in the wake of the attacks, told AFP: "It's sad... In our hearts, we are here, offering support to their (the victims') families."

On Saturday, a fourth plaque is to be unveiled at the site in the southern suburb of Montrouge where Coulibaly gunned down a policewoman.

Commemorations will culminate in a public event Sunday in the Place de la Republique, the vast square that has become the rallying point for "Je Suis Charlie" solidarity and for the mourning after the November 13 carnage.

An oak "remembrance tree" standing some 10 metres (35 feet) tall will be planted in the square.

Veteran rocker Johnny Hallyday will perform "Un Dimanche de Janvier" (One January Sunday), a song recalling the vast march in Paris that attracted 1.6 million people on January 11, 2015.

Dozens of world leaders including British Prime Minister David Cameron, German Chancellor Angela Merkel and Israeli Prime Minister Benjamin Netanyahu attended the march.

Charlie Hebdo had been a target for jihadist attack since publishing cartoons of the Prophet Mohammed cartoons in 2006 and its offices were firebombed in 2011.

Responding to the claims from the bodyguard's widow, Interior Minister Bernard Cazeneuve defended the decision to reduce security at the magazine's offices before the attack, saying the authorities had determined that jihadists had shifted to targeting soldiers and police.

Charlie Hebdo, whose biting, often vulgar humour has spared no religion or political persuasion, will publish a special commemorative edition on Wednesday.

True to form, the cover is unabashedly provocative, featuring a Kalashnikov-toting God figure wearing a blood-stained white robe, under the headline: "One year on: The killer is still at large."

In an editorial, cartoonist Riss, who survived the attack, said his colleagues had been killed "for having dared laugh at religion".