President Donald Trump on Tuesday suggested Mexico with U.S. assistance should “wage war” on the murderous drug cartel “monsters” in response to the brutal killing of multiple Americans a day earlier.

“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,” he wrote on Twitter.

Trump’s remarks came after the news of American citizens getting slaughtered in Mexico, after getting caught in the crossfire of a cartel battle in the border state of Sonora. Relatives have said at least nine U.S. citizens were killed including six children of which two were 7-month-old twins, according to The Associated  Press.

“A wonderful family and friends from Utah got caught between two vicious drug cartels, who were shooting at each other, with the result being many great American people killed, including young children, and some missing,” the president tweeted.

“If Mexico needs or requests help in cleaning out these monsters, the United States stands ready, willing, & able to get involved and do the job quickly and effectively,” Trump added. “The great new President of Mexico has made this a big issue, but the cartels have become so large and powerful that you sometimes need an army to defeat an army!”

Those attacked were members of the LeBaron family, a well-known American clan who has lived in the community in the northern part of the country for decades, according to The New York Times. The attack targeted citizens who live in a community founded as part of an offshoot of The Church of Jesus Christ of Latter-day Saints.

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.

President Trump has raised repeated concerns about levels of gang violence and drug-related crime in Mexico, especially when it comes to securing the U.S .- Mexico border.