Six predominantly black southern churches have burned in the past week, sparking fears that arson attacks are on the rise in the US.

According to officials, at least three of the fires were started deliberately. FBI spokesman Paul Bresson told Buzzfeed News that investigators were working to "determine who is responsible and what motives are behind them.

"I'm not sure there is any reason to link them together at this point," he said on Sunday.

The first incident took place on Sunday 21 June at College Hill Seventh Day Adventist Church in Knoxville, Tennessee. Authorities responded to a call around 9.47pm, and found a van burning in the church carpark. According to local officials, someone set fire to hay bales and bags of compost outside the church, and the building sustained minor damages. WATE 6 reports that it is not being investigated as a hate crime, however, but an act of vandalism. Pastor Cleveland Hobdy III told the station that his reaction was one of "horror".

"When I look at this I see, I think of an intention to try to destroy this entire church. It makes it sad. It's sad either way that someone would put their mind to try to damage a church that's trying to help people," he added.

A second incident occurred on Tuesday 23 June at God's Power Church of Christ in Macon, Georgia. Firefighters were called to the scene early in the morning, the Macon Telegraph reported, and found a side door unlocked. Nobody was injured in the blaze, but local fire chief Marvin Riggins told reporters that the church may be a total loss. The incident has been ruled as arson, but authorities say there is no evidence to suggest yet that it was a hate crime.

A third church suffered an arson attack the following day. Investigators said that a fire at Briar Creek Road Baptist Church on Wednesday 24 June was "intentionally set" and the church sustained some $250,000 worth of damage. Pastor Mannix Kinsey told WCNC that his congregation had already forgiven the perpetrator. "Buildings can be repaired, they can be built over, but the hearts of individuals, this is the opportunity for God to touch the hearts of individuals," he said. Around 60 members of the church attended a service inside the damaged building on Sunday. According to the Charlotte Observer, minister Rev Rhonda Kinsey said their faith was being tested, but "I am standing on your shoulders".

"I am leaning on you," she told those gathered. "Part of our heart was consumed. Thank God, he is a heart fixer."

Glover Baptist Church in Warrenville, South Carolina, was then destroyed by a fire on June 26. The cause of the fire has not yet been determined, but the FBI has joined the investigation. Two further fires at Fruitland Presbyterian Church, in Gibson County, Tennessee, and College Heights Baptist Church in Elyria, Ohio are believed to have been caused by a lightning strike and problems with electrical wires.

The spate of fires follow the shooting of nine members of Emanuel African Methodist Episcopal Church in Charleston, South Carolina, on 17 June. Suspect Dylann Roof, 21, has been charged with their murder, and the incident has once again raised the issue of racial tolerance in the US. Roof had written a manifesto online in which he said he had "no choice" but to kill black people.

"I have no choice. I am not in the position to, alone, go into the ghetto and fight. I chose Charleston because it is most historic city in my state, and at one time had the highest ratio of blacks to Whites in the country," he wrote.

"We have no skinheads, no real KKK, no one doing anything but talking on the internet. Well someone has to have the bravery to take it to the real world, and I guess that has to be me."