A 911 call reporting the fire at Hopewell Baptist Church in Greenville came in at about 9:15 p.m. Tuesday, police said. Firefighters quickly extinguished the blaze.
Most of the damage to the 111-year-old church was to the sanctuary, pastor Carilyn Hudson said at a news conference.
"We do believe that God will allow us to build another sanctuary in that same place," she said, though the extent of the damage was unclear.
There were no reports of injuries; no one had been in the building since about 1 p.m. Tuesday, Hudson said.
Investigators continue to collect evidence, and there are no suspects yet, Greenville Police Chief Delando Wilson said at the news conference. Later, Wilson told CNN that police brought in a person of interest Wednesday afternoon and "are interviewing this person to determine if they had any participation in this event or if we can clear them." Police are investigating multiple motives, including that the fire could be a hate crime.
Fire Chief Ruben Brown said an investigation led to the conclusion that the fire was intentional.
"Accidental was ruled out," he said.
The Bureau of Alcohol, Tobacco, Firearms and Explosives is assisting the Mississippi State Fire Marshal's office. The FBI and the ATF will determine the motive behind the fire, Brown said.
Wilson said police are investigating whether the fire was intended to intimidate voters, but he said it was too soon to tell.
"We will use all resources to determine the cause in this case," Wilson said.
An $11,000 reward is being offered for information that leads to an arrest and prosecution.
The west Mississippi city of about 33,000 near the Arkansas border is 78% black, according to the most recent census. Surrounding Washington County is 71% black.
Mayor Errick Simmons said he spoke to some of the church's 200 congregants who were fearful and felt intimidated. They felt the vandalism was not just an attack on the church, but on the black community, he said.
"It happened in the '50s, it happened in the '60s, but we're in 2016 and that should not happen," he said.
Greenville faced another race-based attack in September when someone painted the n-word on the city's boat ramp, Simmons said. He ordered city workers to paint over the pejorative, he said.
Because it's an African-American church, the FBI is working "with our local, state and federal law enforcement partners to determine if any civil rights crimes were committed," said a statement from the FBI's office in Jackson, the state capital.
ATF agents weren't able to enter the structure until midmorning Wednesday because it was still too hot, Frank said.
A GoFundMe account
set up to help the church rebuild had garnered more than 2,300 donations totaling $87,000 by Wednesday evening, far surpassing a $10,000 goal.