Two suspects in the Charlie Hebdo attack in Paris were known to intelligence services and were “no doubt” being followed before the deadly attack, France’s prime minister Manuel Valls says.

Police are involved in a massive manhunt for two brothers involved in the shooting – Said Kouachi, born in 1980, and Cherif Kouachi, born in 1982.

A third man, aged 18, wanted over the attack turned himself in at a police station in Charleville, 230 kilometres north-east of Paris near the Belgium border.

News agency AFP is reporting that the two armed suspects have been ‘located’ in north France.

• Paris suspect hands himself in: reports
• Paris shooting: a tribute to the victims
• ‘Je suis Charlie’: world’s cartoonists take a stand

But while France remained on edge, a policewoman was killed and a city employee critically wounded in a shooting in southern Paris less than a day after the Charlie Hebdo attack.

Police have arrested a man during investigations following the shooting in which a gunman, wearing a bullet-proof vest, opened fire with an automatic rifle.

Witnesses said there was an accident at the scene.

“So a police woman came to record the accident and just suddenly on a little street, the shooter appeared, shot twice, hit her, hit another guy who works for the city, he was injured on the face,” the witness said.

No link has been established with Wednesday’s attack.

Meanwhile, there was a “criminal” explosion at a kebab shop near a mosque in the town of Villefranche-sur-Saone. No civilians were injured.

“It is a criminal act,” a local official told AFP, adding that a police investigation had been opened. No link was suggested to the Charlie Hebdo shooting.

There were also several attacks against Muslim places of worship overnight.

Two French towns were fired upon on, leaving no casualties, prosecutors said on Thursday.

Three blank grenades were thrown at a mosque shortly after midnight in the city of Le Mans, west of Paris, and shots were fired in the direction of a Muslim prayer hall shortly after evening prayers in the Port-la-Nouvelle district near Narbonne in southern France.

In all, seven people have been detained in relation to the Charlie Hebdo shooting, the interior minister said.

It is understood men and women close to the two brothers were being questioned without saying where they had been detained.

There are conflicting reports about whether the 18-year-old is a French national or related to the two suspects still on the run.

BFM TV, citing unidentified sources, said the man decided to go to police after seeing his name on social media.

Hooded attackers stormed the offices of Charlie Hebdo, a satirical weekly newspaper known for publishing cartoons lampooning Islam and other religions, in the most deadly militant attack on French soil in decades.

The identity of one of the men was discovered after he left an ID card in the getaway car, a police source said.

Authorities said Cherif Kouachi was a known jihadist who was tried on terrorism charges in 2008 and served 18 months in prison.

He had been part of an Islamist cell that enlisted French nationals from a mosque in eastern Paris to go to Iraq to fight Americans.

He was arrested before leaving for Iraq to join the militants.

Cherif and Said Kouachi were born in Paris, police said.

Among the Charlie Hebdo staff members seriously injured in the attack was Simon Fieschi.

His Australian girlfriend Maisie Dubosarsky flew to France on Thursday to be with her partner.

“I saw the headline… and I thought he was dead,” Ms Dubosarsky said.

“Then 30 minutes later his mother contacted me and said he was alive and that was the best news I’ve ever heard.”

She said Mr Fieschi was in a coma and in a critical condition after undergoing surgery from a bullet wound to his shoulder.

Anti-terror raids carried out as supporters rally

The police source said anti-terrorism police searching for the suspects and links to them carried out searches in Reims, Strasbourg and Paris as part of the investigation.

A reporter in Reims saw anti-terrorism police secure a building before a forensics team entered an apartment while dozens of residents looked on.

French President Francois Hollande ordered flags to fly at half-mast for three days in France.

A minute’s silence was observed across the country at midday, after which the bells of Paris’ famous Notre Dame cathedral sounded out across the capital.

“Nothing can divide us, nothing should separate us. Freedom will always be stronger than barbarity,” said the president, calling for “national unity”.

Heavy rain at Notre Dame Cathedral where a crowd has started forming for the minute silence. pic.twitter.com/InTUoThiFh

— Imelda Flattery (@Imeldaflattery) January 8, 2015

Meanwhile tens of thousands joined impromptu rallies across France in memory of the victims and to support freedom of expression.

“This is bad for everyone – particularly for Muslims despite the fact that Islam is a fine religion. It risks making a bad situation worse,” said Cecile Electon, who joined 35,000 people at a vigil on Paris’s Place de la Republique.

Some Parisians expressed fears about the effect of the attack on community relations in France, which has Europe’s largest Muslim population.

Security at transport hubs, religious sites, media offices and department stores was tightened after the government increased the terror alert to the highest level.

Thousands of people also attended vigils in Melbourne and Sydney to remember the victims of the shooting.

Fellow Charlie Hebdo staff name victims

Included in the deceased were Charlie Hebdo co-founder and cartoonist Jean Cabut, editor-in-chief Stephane ‘Charb’ Charbonnier, deputy chief editor Bernard Maris, and cartoonists Georges Wolinski and Tignous.

• Paris shooting: a tribute to the victims

Charbonnier began work at the newspaper in 2009 and his work appeared under the title ‘Charb n’aime pas les gens’ (Charb does not like people).

He was not a stranger to controversy. At the time of the shooting he was under police protection after death threats were made against him, sparked by previous Charlie Hebdo publications.

Cabut, 76, better known as ‘Cabu’, was reportedly the highest-paid cartoonist in the world.

One of his cartoon characters was Mon Beauf, a title that became part of the French language to describe a Frenchman who was racist, sexist or vulgar.

UK parliament pays tribute

Hundreds of British MPs, parliamentary staff and journalists gathered in Westminster Hall in London for a two-minute silence in memory of the 12 people killed in the Paris terror attack.

Speaker John Bercow led the vigil as the Big Ben bells tolled twelve noon over the Parliamentary estate and as the event ended said: “Colleagues, thank you for supporting the people of France.”

Politicians from all sides united to hold pens in the air and with many holding banners reading “Je suis Charlie”.

Among the politicians taking part were Commons leader William Hague and Labour deputy leader Harriet Harman.

– with AAP