French prosecutors have opened an investigation after a petrol bomb was thrown at riot police in Paris, with charges of attempted murder of officers vested with public authority. The incident happened on Saturday in Porte de Charenton, south-east Paris, when incendiary devices were thrown at a group of about 15 gendarmes and police officers. The prosecutor’s office said injuries included second-degree burns, shown on mobile phone video and later broadcast by French television. Violence erupted after youth-led protests across Europe, and in France the unrest spread to Marseille, Grenoble, Bordeaux, Lyon and Toulouse on Saturday night. Officials said an estimated 320,000 demonstrators took to the streets, including some in Halloween costume, before masked rioters arrived. More than 770 people were arrested across France for public order offences. In Germany, interior minister Laurent Nuñez called for harsh penalties, while reports said rioters and looters attacked police in Frankfurt with missiles including petrol bombs and injured more than 100 officers. France’s probe is ongoing, with prosecutors investigating the attempted murder allegation following the attack on Paris riot police.