WASHINGTON, D.C. (Nexstar) — Nine members of a Mormon fundamentalist sect were attacked while traveling near the U.S.-Mexico border.

On Monday, the family with Utah ties was driving on a Mexican highway about 100 miles south of Douglas, Arizona, when relatives say their car was hit by a hail of gunfire. Three mothers and six children, including two infants, were killed.

Utah Republican Mitt Romney says many Americans live in that northern part of Mexico.

“It is a very dangerous area because there are drug cartels that are working along the border,” says Romney.

After news of the attack broke, President Trump tweeted: “This is the time for Mexico, with the help of the United States, to wage war on the drug cartels and wipe them off the face of the earth.”

Mexico’s president responded to Trump’s offer, thanking him for his help, but said it is Mexico’s responsibility to deal with this incident.

Romney says with violence from the cartels threatening the U.S., it’s a problem for both countries. He hopes both the U.S. and Mexico can team up to make sure this never happens again.