France has deported 40 foreign imams for "preaching hatred" in the past three years, a quarter of them in the last six months, Interior Minister Bernard Cazeneuve said Monday, according to Fox News.

The minister vowed to clamp down on mosques and preachers inciting hatred after a suspected Islamist beheaded his boss during an attack on a gas factory last week.

The attack, which had the hallmarks of a jihadist act but is also believed to have personal motivations, was the second in six months in France which is battling to curb radicalisation that has seen hundreds of citizens leave to wage jihad in Iraq and Syria.

Any "foreign preacher of hate will be deported," said Cazeneuve, adding that several mosques were being investigated for inciting terrorism and if found to be doing so, "will be shut down".