AFP journalists in the adjacent town of Burton witnessed a large police presence outside the home of the suspected shooter, whom Renye identified as Thomas Jacob Sanford, 40.
Renye and other officials did not provide any further details on Sanford. US media reports said he had grown up in the area and was a military veteran.
Images of the aftermath at the Church of Jesus Christ of Latter-day Saints in Grand Blanc, a suburb of the city of Flint, showed most of the building reduced to ashes.
Photos also showed the truck apparently driven by the attacker into the side of the building, with two US flags on poles in the vehicle’s rear.
FBI special agent Reuben Coleman told the press conference that the FBI was now leading the investigation, and was looking at the attack “as an act of targeted violence”.
Renye earlier said hundreds were inside when the attack commenced, and that more victims may be found among the debris.
Trump called the shooting “horrendous” and said it was “yet another targeted attack on Christians in the United States of America”.
‘Epidemic of violence’
The Church of Jesus Christ of Latter-day Saints, whose leader had died the previous night aged 101, called Monday’s attack a “tragic act of violence.”
“Places of worship are meant to be sanctuaries of peace-making, prayer and connection. We pray for peace and healing for all involved,” it wrote on X.
Founded in 1830, the Mormon church considers itself a Christian body, but bases its doctrines on the Book of Mormon, a text its followers say contains a fuller version of the words of Jesus Christ than that recorded in the Bible.
Based in the western US state of Utah, there are Mormon churches all over the world, with millions of adherents.
The United States, where firearms are readily available, has a long history of gun violence.
But tensions have soared in recent weeks after a series of high-profile attacks, including the assassination of right-wing activist Charlie Kirk in Utah and a deadly shooting at a federal immigration enforcement facility in Texas.
Monday’s attack also comes a month after a mass shooting at a Catholic church and school in Minnesota, in which two children were killed while attending Mass, and several others were severely wounded.
Political divisions have grown even deeper in the wake of the attacks, with Trump launching a campaign to target left-wing groups he accuses of being “domestic terrorists.”
In his Truth Social post Sunday, Trump wrote: “THIS EPIDEMIC OF VIOLENCE IN OUR COUNTRY MUST END, IMMEDIATELY!”
- Agence France-Presse
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