Andres Manuel Lopez Obrador, Mexico's president has categorically rejected US President Donald Trump's offer to help Mexico 'wage war' on the drug cartels using the US Army.

Trump on Tuesday tweeted that he will be willing to send the US army into Mexico to help the country with it's decades old drug cartels war, after at least nine U.S. citizens, including six children, who live in the Mexican border state of Sonora were killed in a shooting attack Monday blamed on drug cartels.

The victims killed on Monday by the drug cartel belong to the LeBaron family - a breakaway Mormon community and as at the time of the attack, 17 of the family members were traveling in three cars from the settlement before drug cartel gunmen opened fire and torched vehicles as the victims burned to death .

Trump on Tuesday 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. 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!,'

'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!,'

Mexico's new president, Andres Manuel Lopez Obrador, who has improved ties with the US and Donald Trump by passing the landmark UMCNA deal and sending over 20,000 Mexican soldiers to patrol the US-Mexico border, rejected Trump's offer of military assistance.

Obrador told reporters in Mexico ;

'I don't think we need the intervention of a foreign government to deal with these cases,' he said.

The White House has also confirmed the two leaders spoke on Tuesday. 

'Today, President Donald J. Trump spoke with Mexican President Andrés Manuel López Obrador to discuss the recent violence in Mexico and efforts to combat the growing violent behavior of cartels and criminal groups in the region,' said White House deputy press secretary Hogan Gidley in a statement.

'President Trump made clear that the United States condemns these senseless acts of violence that took the lives of nine American citizens and offered Mexico assistance to ensure the perpetrators face justice. The two leaders also discussed ongoing border cooperation and the strong bilateral ties between the United States and Mexico,' he added.