French investigators in the department of Vaucluse have launched an inquiry after seven priests in the department received suspicious letters simply containing the words “Allahu Akbar.”

All seven priests received the hand-written letters on December 9th and reported the suspicious letters to the local police who have stated they are taking the matter very seriously.

“Letters written by hand were sent by the Post Office to seven black African priests with their names and the address of the rectory where they live. On the mail is only the word ‘Allah Akbar’ in French and Arabic,” vicar general of the diocese of Avignon Pascal Molemb Emock told French media.

According to a report by La Depeche, the Avignon prosecutor’s office has taken up the investigation in conjunction with local police.

A source close to the investigation told the newspaper, “These are not direct death threats, but in the context of a terrorist threat, this case is taken very seriously.”

One of the priests commented to French broadcaster France 3 said he would be careful but added that he had no intention to stop his work saying, “I am not afraid for myself, I will continue to live alone in my rectory.”

The letters come weeks after a Tunisian illegal immigrant killed three people in a church in Nice and injured several others. The attacker is also reported having yelled “Allahu Akbar” during the attack.

In recent years, churches and priests have been targetted by radical Islamic terrorists in France, such as the attempted terror attack in 2015 by Franco-Algerian Sid Ahmed Ghlam, who murdered a French dance instructor but failed in his attack on his church targets.

The most well-known terror attack against a clergy member in France took place in 2016 when Father Jaques Hamel was murdered and beheaded during mass at a church in Normandy by terrorists affiliated with the Islamic State terrorist group.

Follow Chris Tomlinson on Twitter at @TomlinsonCJ or email at ctomlinson(at)breitbart.com