The religions leaders gathered in Paris in a show of unity in the wake of the attack.

The Paris mosque rector condemned the bloodshed as an act contrary to the teaching of Islam.

"The attack on a religious place, the violation of a human being and the killing of a priest who is respected and protected in our religion - this is an act outside of Islam, an act that all French Muslims condemn and reject," he said.

The Catholic Archbishop of Paris urged unity among all religions to avoid the disharmony Islamic State was trying to sow. 

"We cannot let ourselves be dragged into Daesh's political game which wants to pit us against each other, the children of the same family."

The anti-terrorist unit of the Paris prosecutor's office is investigating the attack in which both killers were shot dead by police.

Officials say one person hass been arrested.