After three churches in central Louisiana were destroyed by fire in little more than a week, civil rights advocates have expressed concern that black congregations are being targeted.

“We must not turn a blind eye to any incident where people are targeted because of the color of their skin or their faith,” said Derrick Johnson, president of the National Association for the Advancement of Colored People (NAACP), in a statement on Monday. He also referred to the fires as “domestic terrorism”.

Three Baptist churches in St Landry Parish – Mount Pleasant, St Mary and Greater Union – burned between 26 March and 4 April. Sheriff Bobby Guidroz has increased security at other houses of worship in the parish, just north of Lafayette and about 100 miles north-east of New Orleans.

Authorities have called the fires “suspicious”. Late last week, Louisiana Fire Marshal H “Butch” Browning said “patterns” had been discovered.

“There certainly is commonality and whether that leads to a person or persons or groups, we don’t know,” he said.

Pastor Freddie Jack, president of the Seventh District Missionary Baptist Association, told CNN on Monday: “At first we thought it might have been an electrical problem but then when the second church … burning occurred I realized it was our sister church … then two days later the third occurred so … [it] made me think that we’re being targeted.”

Ashley Rodrigue, a spokeswoman for the Louisiana fire marshall, said investigators had not concluded the fires were connected.

In the same two-week span, a fire was “intentionally set” at a predominantly white church in Caddo Parish, Louisiana and at a building housing a social justice not-for-profit group in New Market, Tennessee.

At the Tennessee blaze, which destroyed the headquarters of the Highlander Center, authorities found graffiti associated with the white power movement. According to the center’s executive directors, the fire destroyed “decades of historic documents, speeches, artifacts and memorabilia” from the civil rights movement.

According to FBI data, hate crimes have been on the rise in the US since 2015. Johnson tied the fires to “emboldened racial rhetoric and tension spreading across the country”.

“For decades,” he said, “African American churches have served as the epicenter of survival and a symbol of hope for many in the African American community. As a consequence, these houses of faith have historically been the targets of violence.”

In one week in the summer of 2015 there were reports of at least seven fires at black churches in southern states. Foul play was ruled out in several cases. In four cases in which investigators concluded intentional arson was involved, no arrests were made.

On Tuesday morning the House judiciary committee commenced a hearing on Hate Crimes and the Rise of White Nationalism, at the urging of the NAACP.

In Louisiana, Alanah Odoms Hebert, executive director of the state American Civil Liberties Union, said the fires were a “deeply disturbing” reminder of the violence that communities of color face in the south.

“While the investigation into the cause of the fires continues,” she said, “it’s on all of us to speak out against hate and intolerance, and stand in solidarity with the communities affected by these tragedies”.