Trump said Mexico's President Andres Manuel Lopez Obrador had made fighting the drug cartels a big issue

President Donald Trump urged Mexico Tuesday to "wage war," with US help, on the drug cartels believed to have ambushed a group of American Mormons in northern Mexico, killing nine women and children.

"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 wrote in a tweet.

The ambush occurred Monday in Rancho de la Mora, in an area along the border between the states of Sonora and Chihuahua that is notorious for drug traffickers and bandits, a relative of several of the victims said.

Julian Lebaron told Formula Radio in Mexico that his cousin was traveling to the airport with her four children when their van was attacked and set on fire with the victims inside.

Two other vehicles were also found with the bodies of two women and a boy and a girl. At least five other children managed to escape and walk home, Lebaron said.

Trump said Mexico's President Andres Manuel Lopez Obrador had made fighting the drug cartels a big issue, "but the cartels have become so large and powerful that you sometimes need an army to defeat an army!"

"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. We merely await a call from your great new president!"