By Agence France-Presse MEXICO CITY — At least five US citizens, including four children, who live in the Mexican border state of Sonora have been killed in a shooting attack, relatives said Monday. A relative who asked not to be named for fear of reprisals said he had located the burned-out, bullet-ridden SUV containing the remains of his nephew's wife and her four children. Another relative, Julian LeBaron, said on his Facebook page the dead woman was Rhonita Maria LeBaron. She apparently died along with her twin 6-month-old babies and two other children aged 8 and 10. The first relative attributed the attack to drug cartel gunmen and said he saw dozens of heavily armed gunmen near the burned-out vehicle. The man said a convoy of three vehicles had set out Monday from La Mora — a decades-old settlement founded as part of an offshoot of The Church of Jesus Christ of Latter-day Saints — but were attacked by cartel gunmen in what he said may have been a case of mistaken identity. Two of the three vehicles believed to be carrying two women and 13 children were still missing. Authorities in Sonora state and the US Embassy did not immediately respond to requests for comment. The federal Department of Security and Citizens' Protection said security forces were reinforced with National Guard, army and state police troops in the area following "the reports about disappearance and aggression against several people." Jhon LeBaron, another relative, posted on his Facebook page that his aunt and another woman were dead, which could bring the death toll to at least seven. But Jhon LeBaron posted that six of his aunt's children had been left abandoned but alive on a roadside. The families lived in La Mora, about 70 miles (110 kilometers) south of Douglas, Arizona. Many of the church's members were born in Mexico and thus have dual citizenship. It would not be the first time that members of the break-away church had been attacked in northern Mexico, where their forebears settled — often in Chihuahua state — decades ago. In 2009, Benjamin LeBaron, an anti-crime activist who was related to those killed in Monday's attack, was murdered in 2009 in neighboring Chihuahua state.