Churches in the U.S. face a terrifying new reality: They could be attractive targets for terror as shown by the murder of French priest Jacques Hamel on July 26 in Normandy, France, counter-terrorism experts have revealed.

Amid rising threats, many churches in the U.S. are now hiring self-defence instructors for classes or security guards that include off-duty police officers, according to Ryan Mauro, a professor of Homeland Security at Liberty University and national security analyst for the Clarion Project.

"If you are an Islamist terrorist seeking self-glory, executing a priest will bring you more attention than executing an average civilian," Mauro told Fox News.

Although no terror attacks have yet taken place inside a U.S. church, experts say it could just be a matter of time before such an attack takes place.

"I'm pretty sure there will be attacks in the future," said Jeff King, president of International Christian Concern.

Father Josiah Trenham of St. Andrew Orthodox Church in Riverside, California, now has security officers on hand at services after a non-violent incident in April, months before the French attack.

"It is a deep sorrow to live this way in the 'new America,'" he told Fox News. He revealed that his church received a threat followed by an ominous warning in July when a car passed by and a man repeatedly yelled from a bullhorn "Allahu Akbar!"

Even before the attack on the French church last month, U.S. authorities have already warned that churches could be targeted by terrorists.

In February, Khial Abu-Rayyan, 21, of Dearborn Heights, Michigan, was arrested after he told an undercover FBI agent he was preparing to "shoot up" a major church near his home on behalf of ISIS.

A month earlier, the Rev. Roger Spradlin of Valley Baptist Church – one of the biggest congregations in Bakersfield, California – told congregants that they had received a threat written in Arabic.

Last September, a Muslim in combat gear was charged with making a terrorist threat after he entered Corinth Missionary Baptist Church, in Bullard, Texas, claiming that God had instructed him to kill Christians and "other infidels."

A year earlier, police were called to Saint Bartholomew's Catholic Church in Columbus, Indiana, after the church was vandalised with the word "Infidels!" along with a Quranic verse sanctioning death for nonbelievers. Similar graffiti was found that same night at nearby Lakeview Church of Christ and East Columbus Christian Church.

St. Bartholomew Pastor Clem Davis said churches are vulnerable terrorist targets since their mission is to welcome all.

"We don't have metal detectors, people go in and out. Churches are family-orientated, public, tax-supported spaces; so they may appeal to some as a target," he said.