Hollande Says France Foiled 'Terrorist Acts' This Week

France thwarted "terrorist attacks" this week, French President Francois Hollande said on Wednesday.

"This week, we stopped terrorist attacks which could have taken place," Hollande said on trip to Marseille alongside Mexican President Enrique Pena Nieto, adding that the interior ministry would issue a statement on Thursday.

A security source told AFP that four people with an "Islamist profile" had recently been arrested on suspicion of planning an attack somewhere in France, without giving further details.

France remains on edge after the Charlie Hebdo attacks in January where a trio of gunmen killed a total of 17 people starting with a massacre at the satirical magazine.

And last month, a man with suspected links to the Islamic State group spiked his boss's severed head onto the fence of a U.S.-owned gas factory.

Paris has tightened security around sensitive sites such as factories, calling for "maximum vigilance."

But experts have warned it is extremely difficult to defend against attacks on such sensitive sites.

"There is no such thing as zero risk," said Philippe Prudhon, a technical expert at the UIC union of chemical industries.

"If someone really wants to cause harm, it will be difficult to stop him or her. We have to realize that we have been in a fundamentally different environment for the past three years," said Prudhon.