Image copyright Charlotte Fire Department Image caption Authorities have confirmed that at least three of the fire were intentionally set

A series of fires at African-American churches across the US south has prompted the FBI to investigate whether the blazes are related.

Last week six fires hit black churches in Florida, Georgia, North Carolina and South Carolina and Tennessee.

Three have been ruled arsons and the others are still under investigation.

"They're being investigated to determine who is responsible and what motives are behind them," FBI spokesman Paul Bresson told BuzzFeed News.

No one has been hurt in the fires, but many of the churches were completely destroyed.

The Bureau of Alcohol, Tobacco, Firearms and Explosives is also assisting local authorities in the arson investigations.

Image copyright AP Image caption A wing of Briar Creek Road Baptist Church in North Carolina was destroyed in one incident

J Britt Johnson, an FBI spokesman in Atlanta, said the agency is investigating whether the arson at God's Power Church of Christ in Macon, Georgia, was a hate crime.

Mr Johnson said the move was standard procedure for the agency when a church is a target of arson.

"Opening a preliminary inquiry doesn't suggest that a hate crime has occurred, but rather ensures that it is getting additional scrutiny," Mr Johnson said.

The fires came about a week after nine black churchgoers were shot and killed in Charleston, South Carolina in what police called a racially motivated attack.

The tragedy has reignited debate about race relations and sparked a backlash against the Confederate flag.