France PM Manuel Vallis says not all planned terror attacks can be stopped

France is doing all it can to prevent terrorist attacks but there will be more of them, Prime Minister Manuel Valls said on Wednesday following this week's murder of a policeman and his wife by a Frenchman who pledged allegiance to Islamic State.

Valls said the intelligence and police services had foiled 15 attacks since 2013 and were waging a non-stop battle to track down would be terrorists.

"We need to tighten the net and give police and intelligence services all the means they need, but we will witness further attacks," he said on France Inter radio.

"More innocents will lose their lives," he said.

A memorial ceremony is planned Wednesday in Manganville for Jean-Baptiste Savaing, the 42-year-old police commander who was stabbed outside his suburban house Monday night, and his 36-year-old female companion, a police administrator whose name has not been released.

President Franois Hollande is joining a moment of silence at the Interior Ministry on Wednesday.

Attacker Larossi Abballa, who had a past terrorist conviction, recorded a video during the attack before being killed in a police raid.