The FBI has been called in to investigate fires at three African American churches in Louisiana over the past fortnight.

Police say that there is a "clear pattern' linking the incidents in St Landry Parish, 63 miles east of the state capital, Baton Rouge.

"We're very cognisant that there's a problem, and there's no coincidence that there are three fires," said H. "Butch" Browning, Louisiana's state fire marshal.

The first fire took place on March 26, with two more taking place over the past week.

All the fires were started in the middle of the night when the churches were empty.