New video footage has emerged of the Paris gunmen on the streets of the city carrying out their attack on Charlie Hebdo.

The footage shows the two masked figures calmly returning to their getaway vehicle after murdering staff at the satirical magazine.

The pair reload their weapons, before one shouts: "We have avenged the Prophet Mohammed, we have killed Charlie Hebdo."

It then shows the gunmen firing on a police car as they made their escape.

The vehicle, lights flashing, is forced to reverse at speed as the killers get out of their own car, aim their weapons and open fire.

The fundamentalist brothers Said and Cherif Kouachi killed 12 people in last Wednesday's deadly attack on Charlie Hebdo, including two policemen.

One of the officers was shot at point-blank range as he lay wounded on the ground.

Their accomplice, Amedy Coulibaly, gunned down a police officer before killing four people in a Jewish supermarket in the French capital.

All three died in shoot-outs with police on Friday.

In the wake of the atrocities, France's Prime Minister has announced he would seek tighter surveillance of convicted extremists, amid reports the weapons used to kill 17 people came from outside the country.

Manuel Valls said "serious and very high risks remain" and warned the French not to let down their guard.

Christophe Crepin, a French police union representative, said several people were being sought in connection with the "substantial" financing of the attacks.

The funding and logistics involved indicated an organised network, he said.

French police say as many as six members of the terror cell behind the attacks may still be at large.

The Bulgarian authorities said they had arrested a French citizen, Fritz-Joly Joachin, believed to have links to one of the Kouachi brothers.

Meanwhile, funerals have taken place in Paris and Jerusalem for some of the 17 killed in the terror attacks, including the three murdered police officers.

And the magazine targeted by the terrorists is preparing for its biggest ever print run of its special 'survivor's edition'.

Three million copies will be printed of the latest issue, which will have a cartoon of the Prophet Mohammed on its front cover.

Charlie Hebdo staff said they wanted to show they would not "cede" to extremists trying to silence them.

The head of Europol has warned up to 5,000 EU nationals pose a potential terrorist threat to Europe after travelling overseas to countries like Syria.