A woman carrying an AR-15-style rifle and accompanied by her young son opened fire at a megachurch in Houston, Texas, before being killed by off-duty police officers.
Her weapon had “Free Palestine” written on it to carry out the shooting on Sunday, CNN reported, citing a federal law enforcement source.
The woman's child, whom police said was aged seven, and a man in his 50s were injured in the attack. The boy is in a critical condition after being shot in the head.
The incident occurred at Lakewood Church, which has the capacity for about 17,000 worshippers and is led by famous televangelist Joel Osteen.
The shooter was identified as 36-year-old Genesse Ivonne Moreno in an affidavit seeking a search warrant for a home in Conroe, about 64km north of Houston, the Associated Press reported, citing court documents.
Ms Moreno entered the church about 2pm, shortly before the Spanish-language service began, wearing a trench coat and backpack with a "detonator cord", Houston Police chief Troy Finner said.
Two off-duty police officers providing security during the service shot the woman.
After she was shot, the woman told police she had a bomb but authorities said no explosives were found when her vehicle and backpack were searched, the Associated Press reported.
Chief Finner said she had been seen spraying “some type of substance on the ground”, but police said on Monday that the substances being used were benign.
Investigators are trying to determine whether the shooting was politically motivated, the law enforcement source told CNN.
It is unknown who fired the shots that injured the child.
“I will say this: that female, that suspect, put that baby in danger,” Chief Finner said. “I’m going to put that blame on her.”
He added the violence “could have been a lot worse” had the two off-duty officers not intervened.
About 45,000 people a week attend services at Lakewood Church, making it the third largest church in the country.
Mr Osteen said his congregation was “devastated” and he would pray for the victims, their families and for the woman who carried out the shooting.
“We’re going to stay strong and we’re going to continue to move forward,” he said.