French President Francois Hollande attends a national tribute at Paris Prefecture for the three officers killed during last week's attacks by Islamic militants, January 13, 2015. The three police officers were killed in the terror attacks at the offices of satirical weekly Charlie Hebdo and in the streets of Montrouge, outside the French capital. [Photo/Agencies]

At police headquarters in Paris, French President Francois Hollande paid separate tribute Tuesday to the three police officers killed in the attacks, placing Legion of Honor medals on their caskets.

"They died so that we could live free," he said, flanked by hundreds of police officers.

Hollande vowed that France will be "merciless in the face of anti-Semitic, anti-Muslims acts, and unrelenting against those who defend and carry out terrorism, notably the jihadists who go to Iraq and Syria."

As Chopin's funeral march played in central Paris and the caskets draped in French flags were led from the building, a procession began in Jerusalem for the four Jewish victims of the attack Friday on a kosher supermarket in Paris.

French police say as many as six members of the terrorist cell that carried out the Paris attacks may still be at large, including a man seen driving a car registered to the widow of one of the gunmen. The country has deployed 10,000 troops to protect sensitive sites, including Jewish schools and synagogues, mosques and travel hubs.