Mexican President Felipe Calderon has called on US presidential hopefuls to stop verbally attacking illegal Mexican immigrants to score political points.
Calls have grown in the US for tighter border security
Candidates were taking Mexicans as "symbolic hostages" in speeches and debates on immigration issues, he said.
Mr Calderon said he was worried by what he called the "growing harassment" and "persecution" of Mexicans in the US.
Illegal immigration is among US voters' top concerns and is set to be a key issue in the 2008 presidential poll.
It is estimated some 12 million illegal immigrants live in the US, many of them from Mexico.
In a speech to an agency representing migrants, Mr Calderon said his government's duty was to protect the rights of Mexicans living abroad.
"I am especially concerned at the growing harassment and in recent days the persecution of Mexicans in the US," Mr Calderon said.
"It is my duty to call respectfully but firmly on the candidates of the political parties in the US to stop taking Mexicans as symbolic hostages in their speeches and strategies."
Mr Calderon's remarks seemed aimed both at the hard line some candidates have taken on the immigration issue and the reluctance of other candidates to take clear positions in the debate, correspondents say.
The Mexican president outlined steps his government planned to take to help Mexican migrants, including a project to expand shelters for people deported back across the border.
His government would also launch media campaigns to increase the awareness of the contributions migrants make to US society, Mr Calderon said.
US President George W Bush's attempts to overhaul immigration laws collapsed amid heated debate in Congress earlier this year.
The question of how to address illegal immigration, without alienating the large Hispanic electorate, is a tricky political issue for candidates.
The debate has also touched on questions of national security, with several candidates arguing there is a need for tougher border controls to prevent potential terrorists entering the country.
Among them is Republican outsider Tom Tancredo, who this week released a hard-hitting campaign advertisement that appears to associate illegal immigrants with extremism.
The advertisement shows images of a hooded man in a crowded shopping centre and clips of bombings in Europe as the narrator says:
"There are consequences to open borders beyond the 20 million aliens who have come to take our jobs.
"Islamic terrorists now freely roam US soil, jihadists who froth with hate, here to do as they have in London, Spain, Russia.
"The price we pay for spineless politicians who refuse to defend our borders against those who come to kill."