French counter-terrorism units seized a rocket launcher besides an arsenal of weapons during an overnight raid in Lyon. The seizure has raised fears that the Islamic State (Isis) terrorists could be planning more attacks in France.

Besides the rocket-propelled grenade (RPG) - which is a shoulder-fired, anti-tank weapon system that fires rockets equipped with an explosive warhead - the counter-terrorism units also found a Kalashnikov assault rifle (AK 47), handguns and bulletproof vests.

French daily Le Figaro said 15 handguns and eight other "weapons of war" were seized in the 168 raids across the country.

In all, 31 weapons have been seized , while 104 people with suspected jihadi links are under house arrest, the French Interior ministry said.

At least five people have been arrested and taken into custody after the weapons were found at their homes, BFM TV reported.

France announced that the anti-terror raids were carried out in Lyon, Toulouse, Grenoble, Jeumont, Strasbourg, Marseille, Lille, the neighbouring commune of Roubaix and the Parisian communes of Bobigny and Saint-Denis.

French Prime Minister Manuel Valls warned that more terror attacks could take place within "days or weeks to come." He also revealed that the attacks in Paris, which killed at least 129 people and injured more than 400 on Friday night were planned in Syria.

The Islamic State terrorists have time and again threatened to carry out attacks on French soil. The Sunni terrorist group had asked Muslims in the country to wage attacks on France as an act of their "holy war."

Last  year, an Isis video had featured several French nationals, who in turn had urged the Muslims in Western countries to 'poison' the food and use any weapon possible against the "enemies of Islam."

Within months of it, Isis supporters in Paris carried out a series of attacks, including the one involving the shooting at the office of the Charlie Hebdo magazine that left 12 people dead.