MEXICO CITY (AP) — Sen. Mitt Romney says he’s been briefed on the slaying of nine U.S. citizens in northern Mexico and calls it “a great tragedy” and something “really unthinkable.”

The Republican from Utah said Tuesday that the attacks were probably “associated with the business of the cartels” rather than a targeted attack on the U.S.-affiliated religious community.

He said he agrees with President Donald Trump that “Mexico has to really knuckle down and go after some of these cartels and stop this escalating level of violence.”

The victims are members of a faction that long ago broke away from The Church of Jesus Christ of Latter-day Saints and some have family ties in Utah.

Romney’s own father was born in a similar but different group in northern Mexico. He said he doesn’t know any of the people involved.