Terror wave in France may not end soon: Expert

"Many European youth have left their home to receive training in Iraq [under the ISIS]. Around 700 are still fighting there and it is believed that 200 of them have returned. These people are highly trained and they have weapons," Agha told ANI.

"The attack yesterday proves that the militants were highly trained and had access to police weaponry. They are trained in guerrilla warfare and I think that France is in trouble. This does not seem like it will end soon. At the same time, the French government is also determined to eradicate this problem from the country," he added.

Earlier in the day, a police officer was shot dead by an unknown gunman, with a bystander left critically injured.

This incident follows Wednesday's attack on Charlie Hebdo, which left 12 people dead, including two police officers, with a further five wounded.