PARIS (AFP) - President Francois Hollande told grieving relatives of three police officers killed in Islamist attacks that they had "died so that we could live in freedom", as he decorated them posthumously in an emotional ceremony Tuesday.

Colleagues and family members broke down in tears as Hollande said the whole of France "shared their pain" after the three officers were gunned down in a series of Islamist attacks.

As the Marseillaise national anthem echoed around the square of the Paris police headquarters, a grim-faced Hollande gently laid the Legion d'honneur medal on the trio of coffins draped in the French flag.

"They died carrying out their duty with courage, bravery, dignity. They died as police officers," he said.

"I assure you that the whole of France shares your pain," Hollande told the victims' mourning relatives.

In a defiant message, the president added: "Our great and beautiful France will never break, will never yield, never bend" in the face of the Islamist threat that he warned was "still there, inside and outside" the country.

Under grey skies, pallbearers marched slowly through the square to the strains of a funeral march and past a huge French flag fluttering in the breeze.

Hollande paid tribute to Ahmed Merabet, a 40-year-old Muslim policeman, who was "executed in a cowardly way" by the killers as he lay wounded on a Paris sidewalk as they fled the offices of the Charlie Hebdo satirical magazine on Wednesday.

"Ahmed Merabet, a French Muslim, was very proud to represent the values of the Republic, secularism. He knew better than anyone that fanaticism kills Muslims. It's true in Africa, in Iraq, in Syria. In France," Hollande said.

The other police officers killed were Franck Brinsolaro, 49, who was assigned to protect Charb, the lead cartoonist at Charlie Hebdo, where 12 were killed on Wednesday at the beginning of three days of terror in the French capital.

"He died with his weapon in his hand. The others had only their pens. He died for freedom of speech," Hollande said of Brinsolaro.

Clarissa Jean-Philippe, 26, from the French Caribbean island of Martinique, was gunned down by Amedy Coulibaly as she confronted him on a patrol. Coulibaly later killed four Jewish shoppers in a kosher supermarket.

"How can we ever comprehend that an assassin can commit such an abomination? Just because she wore a uniform - the symbol of the Republic," Hollande said.