Mexican President-elect Felipe Calderon has met US President George W Bush to voice concern over US plans to fence off part of the two countries' border.
Mr Calderon has likened the fence plan to the Berlin Wall
Mr Bush later said he had assured the visiting Mexican leader the two countries would co-operate closely.
As well as migration issues, the two men discussed free trade and efforts to curb drug trafficking.
Mr Calderon had earlier said he hoped the Democrats' new majority in Congress would boost US immigration reforms.
Mr Calderon was making his first visit to the White House since beating left-wing challenger Andres Manuel Lopez Obrador in Mexico's recent close-run election.
His visit follows mid-term elections this week that saw Mr Bush's Republican Party lose control of both houses of Congress.
Mr Calderon said he had used the meeting with President Bush to express his concern over the US stance on immigration.
"President Bush was very open to all the arguments that I presented to him," he said.
Mr Calderon has called US plans to build a 700-mile (1,125km) border fence "deplorable", and even made comparisons with the Berlin Wall.
Speaking at a gathering of Hispanic leaders in Washington, Mr Calderon said that the two countries needed "bridges for progress and not walls that isolate and divide".
The border "should not be a zone of barbed wire, but a zone of opportunities," Mr Calderon added.
Mr Bush signed the plan for a fence into law despite strong Mexican opposition in October.
Washington is hoping that the plan will stem the tide of illegal immigrants into the US.
About 11 million Mexicans are thought to live in the US, more than six million of them illegally.
An estimated 1.2 million illegal immigrants were arrested last year trying to cross into the US via the border states of Texas, New Mexico, Arizona and California.
BBC Americas analyst Will Grant says it is too early to say how the new Democratic majority in Congress will affect plans for the border fence.
In order to get the bill through, Mr Bush had to calm conservative fears over his plans for a guest-worker programme which opponents said was akin to an amnesty for illegal immigrants.
A Democrat-led Congress will certainly be more sympathetic to the guest-worker idea, our correspondent adds, they will also probably ask Mr Bush the difficult questions about the barrier's funding.