(AP) — Houses of worship are meant to be places of shelter, reflection and peace, where strangers are welcome. But the recent string of high-profile mass shootings in the U.S. is a reminder violence can happen anywhere, prompting some faith leaders to ramp up security.

Today an armed police officer watches over Sunday services at Mt. Zion African Methodist Episcopal Church in Charleston, South Carolina, said the Rev. Kylon Middleton, who leads the congregation. When an officer is unable to be on campus for church events, members carrying concealed weapons keep watch.

“It is sad, but we are in such times where we must have armed security to protect our people,” he said.

The church is two blocks away from Emmanuel African Methodist Episcopal Church. In 2015, a self-proclaimed white supremacist opened fire during Bible study and killed nine worshippers, including the senior pastor. Middleton said the late pastor was like a brother to him.

In the wake of the massacre, security discussions at Mt. Zion factor worship style into the equation, including the need for some to always keep their eyes open, especially when most have theirs closed in prayer, Middleton said.

Historically, sanctuaries have been vulnerable to violent attacks — from bombings at Black churches during the Civil Rights era to more recent shootings in the U.S. at mosques and Sikh gurdwaras. In the U.S., FBI hate crime statistics show that incidents in churches, synagogues, temples and mosques increased 34.8% between 2014 and 2018.

Past attacks on houses of worship and other public spaces have prompted faith leaders to evaluate — sometimes for the first time — if there is more that can be done to keep their flocks safe.

“No one ever thought mass shootings would happen in churches which are sacred sanctuaries where you can escape the world and seek spiritual refuge,” he said. “When that space has been violated, it creates a restlessness of spirit.”