Mourners embrace outside Morris Brown AME Church before attending a vigil the day after a mass shooting in Charleston, South Carolina, June 18, 2015. Reuters

New York Mayor Bill de Blasio pledged to strengthen security at local black houses of worship after a white man opened fire inside a historic church in Charleston, South Carolina, killing nine people. De Blasio said the New York City Police Department would increase patrols at New York churches after the Wednesday-night mass shooting at Emanuel African Methodist Episcopal Church in Charleston's historic downtown district.

“I want everyone to know there’s no place in New York City for this kind of hatred,” he said, according to local media reports. “And that we -- through the NYPD -- have increased our resources directed at protecting African-American churches in this city as a precaution.”

De Blasio said there were no known threats to city churches, but that officers would visit local houses of worship Thursday to ensure safety, NBC News reported. The South Carolina suspect, 21-year-old Dylann Roof, was arrested Thursday morning in Shelby, North Carolina.

"We in this city feel the pain of people anywhere in this country, anywhere in this globe, because we’re so connected to each and every part of the country and the world," De Blasio said. "There are so many people here who hail from South Carolina, and it’s a very, very painful moment for all of us."

Some local church leaders were also on alert. The Rev. Herbert Daughtry of Brooklyn's House of the Lord said police officers hadn't visited his church as of early Thursday afternoon, but he had reminded church leaders to be vigilant of any suspicious behavior, Newsday reported.

"Even Jesus said, 'Watch as well as pray,' " Daughtry said. "Even Jesus taught us to be alert. You don't have to always pray with your eyes closed."

Roof reportedly entered the Charleston church, asked for the pastor and sat next to him during Bible study for about an hour before opening fire. “I have to do it,” he said. “You rape our women and you’re taking over our country. And you have to go.”