Michigan, USA – A gunman drove a vehicle through the front doors of a Church of Jesus Christ of Latter-day Saints building in Grand Blanc Township, Michigan, USA  on Sunday before opening fire on worshippers, killing at least four people and injuring eight others, according to police.

Officials identified the suspect as Thomas Jacob Sanford, 40, of Burton, Michigan. He was shot and killed by officers in a parking lot behind the church shortly after the attack. Police said Sanford used an assault rifle and also appeared to have deliberately set a fire inside the building, which was later extinguished. Authorities warned that more victims could be found inside.

Investigators said as many as three improvised explosive devices were recovered from the scene. The FBI, now leading the investigation, is treating the incident as “an act of targeted violence”, according to Reuben Coleman, special agent in charge of the bureau’s Detroit field office, NBC reported.

Sanford, who had a military background, reportedly began firing at worshippers after crashing his vehicle into the church entrance during Sunday service. Grand Blanc Township and Burton are suburbs of Flint in the US state of Michigan.

Authorities are still working to establish a motive and have cordoned off the area while bomb squads and forensic teams continue to examine the site.