One of the biggest manhunts in recent French history is under way after four people were shot dead at a Jewish school in Toulouse.
Police have linked the attack to two shootings last week in which three soldiers of North African descent died.
The same gun and the same scooter were used in all the attacks, but the gunman has not been identified, officials say.
President Nicolas Sarkozy has placed south-western France on the highest level of terrorism alert.
It is the first time in the country's history that "scarlet alert" has been declared.
The measure enables the authorities to disrupt daily life and implement sweeping security measures, including mixed police-military patrols, powers to suspend public transport and close schools.
Guards are being posted outside all faith-based schools, as well as all Jewish and Muslim religious buildings.
Thousands of people marched through the streets Paris on Monday evening in memory of the victims.
All French schools will observe a minute's silence on Tuesday at 11:00 (10:00 GMT).
A team of about 200 investigations from Paris is pursuing two main lines of inquiry - an Islamist motive or the far right.
But Interior Minister Claude Gueant told French radio the authorities did not know who the killer was.
"For now, we carry on working. We're no further than that," he said.
The minister said "a witness saw a small video camera around the killer's neck" and the authorities were combing the internet for any possible footage.
A teacher and three children were shot dead at the Ozar Hatorah school in Toulouse, and a teenage boy was seriously injured.
The shootings took place as parents were taking their children to the school on Monday.
"This man alighted from his moped and, as he was outside the school, he shot at everybody who was near him, children or adults," local prosecutor Michel Valet told journalists.
The scooter - a black Yamaha - was stolen in Toulouse five days before the first shooting. Its number plate was picked up by closed-circuit TV cameras at the school, police sources said.
The dead were Jonathan Sandler, a 30-year-old rabbi and teacher of religion originally from Jerusalem, and his two sons, aged three and six.
The fourth person killed was a seven-year-old girl, Myriam Monsonego, daughter of the head teacher. She died in her father's arms
Mourners in Toulouse gathered at the school for an overnight vigil, while in Paris, thousands took part in a silent march to show their sympathy for the victims. There was also a remembrance service at the Nazareth synagogue in the French capital.
All the dead were dual French-Israeli nationals and will be buried in Israel, the Israeli foreign ministry said.
A 17-year-old boy was seriously hurt. Initially, the killer used a 9mm gun, but when it jammed, he switched to a .45 calibre pistol.
Police say the .45 was the same gun used to kill three soldiers in two separate shootings in Toulouse and nearby Montauban last week. All three were of North African or Caribbean origin.
The mother of a girl at the Toulouse school told the BBC she was angry with the authorities who she said had not taken last week's incidents seriously enough and had "lost time to look for this man".
The BBC's Hugh Schofield in Paris says not since the early 1980s have there been lethal attacks like this in France on Jewish targets. And even then, children were never the primary victims, he says.
All the candidates in the French presidential election have suspended campaigning.
Mr Sarkozy said his campaign would remain suspended until Wednesday at the earliest, when he is due to attend the soldiers' funerals.
As well as Mr Sarkozy, opposition Socialist candidate Francois Hollande visited Toulouse to offer his condolences. Far-right candidate Marine Le Pen called on the authorities to do everything to prevent another such attack.
- French gun suspect 'wants to die'
- Raid on Toulouse shooting suspect
- Queen addresses both Houses of Parliament for first time in a decade as peers
- Call for hairdressers to get skin cancer training
- Huge layoffs at Oprah's OWN network as she fires 30 of her staffers
- Egypt's Coptic Christians hold second vigil for Pope Shenouda
- Private cash needed to boost roads network, says David Cameron
- France shooting: Jewish school in Toulouse attacked
- Swiss bus crash: Belgium prepares to repatriate bodies
- I Can't Find Love - Prince Harry
- Belgium coach crash in Switzerland tunnel kills 28
- French election: Le Pen set to join presidential race
- Locked-in syndrome' patient awaits ruling on death
- Anders Behring Breivik case: Police quiz killer's father
- Women's Day gets Google Doodle
- Russia election: Monitors refuse to recognise Putin win
- Nicolas Sarkozy says France has too many foreigners
- EU summit: All but two leaders sign fiscal treaty
- Turkey: Ten wounded in Istanbul police bus blast
- Strauss-Kahn freed by police in prostitution inquiry
- Greece bailout: Large protests expected against cuts
- Australia's Foreign Minister Kevin Rudd resigns
- Strauss-Kahn 'a suspect' in prostitution ring inquiry
- Pay-per-Neet' scheme aims to help teenagers find work
- Eurozone ministers back 130bn-euro bailout for Greece