President Barack Obama has promised the US will stand alongside Mexico in its fight against drug-related violence.
The vow came after talks with President Enrique Pena Nieto in the White House, in which the two discussed the recent disappearance of 43 Mexican students.
The students were believed to have been handed over to a drugs gang. The case sparked protests around Mexico and more were held outside as the leaders met.
Mr Obama called it a "tragic" case and said he supported Mexico's response.
The US president said his country would be a "good partner" to its neighbour in the fight against drugs and associated problems.
"Our commitment is to be a friend and supporter of Mexico in its efforts to eliminate the scourge of violence and drug cartels that are responsible for so many tragedies inside of Mexico," he said.
Earlier this week, the wife of the former mayor of the Mexican city where the students went missing was charged with organised crime and money laundering.
Prosecutors say police handed the students over to the drug gang and the gang killed them.
At the scene: Thomas Sparrow, BBC Mundo, Oval Office
The disappearance of 43 students in late 2014 has tarnished the image of the Mexican government and enraged many Mexicans.
The issue dominated discussions between the two presidents at the Oval Office and, as they talked, dozens of protesters defied the first snowfall of the year to demand justice.
Many shouted slogans in Spanish like "they were taken away alive, we want them back alive". Others had posters that read "we want a better Mexico, without deaths and disappearances".
Ultimately, what many want is answers from the government - where the students are and what exactly happened to them.
On Monday, Human Rights Watch also added to the pressure on Pena Nieto by highlighting Mexico's "human rights' crisis" and asking the president to address the issue more seriously.
The two presidents spoke for about an hour on several issues including border security and Cuba.
Mr Pena Nieto was visiting the White House for the first time as president and he backed Mr Obama's new policy on immigration - granting legal status to millions of undocumented migrants, many of them Mexican.
But the battle against drugs and its consequences dominated the meeting.
Tens of thousands of people have been killed in drug-related violence in Mexico in recent years.