As a search for the assailants and the prisoner they freed stretched into a second day, the authorities said the assault was surprising given that the inmate was not high-profile.
Hundreds of police officers in France were searching on Wednesday for an escaped inmate and the armed assailants who freed him during a violent ambush of a prison convoy a day earlier, an attack that left two guards dead, deeply shocked the nation and set off protests by prison guards around the country.
“We’re putting considerable resources into it,” Gérald Darmanin, France’s interior minister, told RTL radio the morning after the ambush, which a small group of assailants staged at a tollbooth on a major highway about 85 miles northwest of Paris.
Over 450 officers, he said, have searched the area of the country where the assailants used two cars to block the prison convoy before emerging with automatic weapons and firing repeatedly, killing two guards and injuring three others before fleeing with the freed inmate.
Mr. Darmanin said it was unclear how many assailants had taken part in the ambush, although security camera footage and bystander videos that were spread on social media after the attack suggested that there were at least five. He did not say whether investigators had identified them.
Mr. Darmanin said riskiness of the attack and the amount of preparation that appeared to have gone into its planning were surprising, given that the inmate who was freed — Mohamed Amra, 30 — was not high-profile, despite a lengthy criminal record.