Eighty-five-year-old Father Jacques Hamel was stabbed by two Islamic State-linked terrorists during morning mass at a church in the commune of Saint-Etienne-du-Rouvray.
President Francois Hollande has attended an interfaith meeting which was supported by Christian, Jewish, Muslim and Buddhist leaders.
The government's defence committee has announced 23,500 police officers, military personnel and reservists are going to be mobilised this summer to help protect the country.
Meanwhile, it has emerged one of the men involved in Tuesday's stabbing had previously been arrested on two separate occasions for attempting to use the identities of his relatives to join extremists in Syria.
France's anti-terrorism prosecutor said 19-year-old Adel Kermiche had been wearing an electronic surveillance tag but it was deactivated for a few hours every morning, corresponding with the time Fr Hamel was attacked.
Claiming France was "waging war", Mr Hollande pledged to fight Islamic State "using all means possible", adding: "What terrorists want is to divide us, separate us, set us against each other. We will win this war."
Mr Hollande yesterday visited the scene of the stabbing in Saint-Etienne-du-Rouvray where he met with emergency and security services personel.
Tuesday's attack came twelve days after a Tunisian national ploughed into crowds along the promenade in Nice on Bastille Day, killing 84 people.
It also follows earlier atrocities targeting concert-goers and sports fans in Paris last November, and the Charlie Hebdo magazine in the capital in January 2015.