Image copyright @LAFIREMARSHAL

Prosecutors have filed new hate crime charges against a white man accused of burning down three African-American churches in the US state of Louisiana.

Holden Matthews, 21, the son of a local sheriff deputy, learned of the new charges during a court appearance on Monday when he pleaded not guilty.

During the hearing, the judge denied his bond request due to a "substantial amount of evidence" against him.

Officials had not previously cited race as a possible motive.

Louisiana Fire Marshal Butch Browning said on Monday the suspect - who has no previous criminal record - should not be released because he presents "an immediate risk to public safety".

"In my mind, I felt another fire was imminent," Mr Browning said, describing the evidence investigators have found against Mr Matthews.

All three fires were started with gasoline and occurred around Opelousas, about 60 miles (100km) west of the state capital of Baton Rouge.

Among evidence presented during the pre-trial appearance, in which Mr Matthews was displayed on video feed from jail, Mr Browning testified that the suspect documented his alleged crimes through videos and photos on his phone.

After he was arrested, prosecutors found pictures of the flames that appeared to have been taken before firefighters arrived to extinguish them.

They also found news reports on his phone in which he had superimposed himself on those reports in order to claim responsibility while talking to a friend online.

"He actually superimposed himself on those news reports, claiming responsibility for these fires," Mr Browning said.

Location data from his mobile phone and surveillance footage of his vehicle also tied him to each of the crime scenes.

Image copyright CBS Image caption Debris at one of the church fires in Louisiana's St Landry Parish

Mr Matthews was arrested last week and charged with arson of a religious building before the state hate crime charges were added.

His arrest came over two weeks after the first fire broke out at the St Mary Baptist Church, followed by the Greater Union Baptist Church and Mount Pleasant Baptist Church in Opelousas, which were each more than 100 years old.

During the search for a suspect, Governor John Bel Edwards said the attacks in the southern state were a reminder "of a very dark past of intimidation and fear".

During Monday's hearing, in which the suspect never spoke and entered his not guilty plea through a lawyer, investigators mentioned the suspect's connection to black metal music.

He said that Mr Matthews had recently posted on Facebook about the Lords of Chaos - a film about a Norwegian black metal band that committed acts of violence in the 1990s.