French President François Hollande has used a ceremony to honour a police officer slain in Paris last week to call for unity in the "long and difficult fight against terrorism".
He awarded Xavier Jugelé, 37, the Legion of Honour, one of France's highest honours.
The two candidates to succeed Mr Hollande, Emmanuel Macron and Marine Le Pen, both attended.
They will face off at a second round of voting on 7 May.
Mr Jugelé, 37, was killed with a Kalashnikov rifle while on duty on the Champs Elysées avenue last Thursday, The main suspect is convicted criminal Karim Cheurfi.
"Once again France has lost one of its bravest sons," Mr Hollande said. "Once again the Republic has lost one of its most valuable guardians."
He said France's struggle against Islamist terrorism was "a fight that is going to last, a fight that will be waged until the threat is completely neutralised".
Mr Jugele's partner, Etienne Cardiles, gave a moving tribute to his loved one, who had campaigned for gay rights and volunteered in Greece to help with the migrant crisis.
"I suffer without hatred," he said.
The issue of security sharply divides the presidential candidates, who were appearing together in public for the first time, though discreetly.
They were among a large group of politicians and public figures who watched as the flag-draped coffin was brought into the courtyard of police headquarters.
Ms Le Pen wants France to reintroduce border controls and deport all foreigners on a terror watchlist.
Mr Macron, an advocate of open borders, has urged French citizens not to give in to fear.
Originally from the Loire Valley region in central France, he had reportedly been serving in the capital since 2014.
On 13 November 2015, he was deployed to secure the area around the Bataclan concert hall after the attack by the so-called Islamic State group.
When the venue reopened last November with a concert by Sting, Mr Jugelé was there again, telling the US magazine People: "I'm happy to be here... We're here tonight as witnesses. Here to defend our civic values. This concert's to celebrate life. To say no to terrorists."
Recent terror attacks in France
- 7-9 Jan 2015 - Two Islamist gunmen storm the Paris offices of satirical magazine Charlie Hebdo, killing 17 people. Another Islamist militant kills a policewoman the next day and takes hostages at a Jewish supermarket in Paris. Four hostages are killed before police shoot the gunman dead. The other two gunmen are cornered and killed by police in a siege.
- 13 Nov 2015 - IS jihadists armed with bombs and assault rifles attack Paris, targeting the national stadium, cafes and Bataclan concert hall. The co-ordinated assault leaves 130 people dead, and more than 350 wounded.
- 13 Jun 2016 -A knife-wielding jihadist kills a police officer and his partner at their home in Magnanville, west of Paris. He declares allegiance to IS, and police later kill him.
- 14 Jul 2016 - A huge lorry mows down a crowd of people on the Nice beachfront during Bastille Day celebrations, killing 86. IS claims the attack - by a Tunisian-born driver, later shot dead by police.
- 26 Jul 2016 - Two attackers slit the throat of a priest at his church in Saint-Etienne-du-Rouvray, in Normandy. They are shot dead by police.
- 3 Feb 2017 - A machete-wielding Egyptian man shouting "Allahu akbar" attacks French soldiers at Paris's Louvre Museum - he is shot and wounded.
- 20 Apr 2017 - A known terror suspect opens fire at police on the Champs Elysées in Paris, killing one and wounding two. He is shot dead - and the assault is claimed by IS.