Mexico's Congress has condemned what it says is a border violation by US workers building a controversial barrier between the two countries.
Many Mexicans see the border barrier as offensive
Legislators say workers and equipment building a section of the barrier have gone 10 metres (yards) into Mexico.
The alleged border violation comes ahead of a high-level meeting in the Canadian capital Ottawa.
US, Mexican and Canadian foreign ministers are to discuss border security and trade issues.
Mexican legislators said they had photographs and video, taken on Monday, of the workers and heavy-duty construction equipment that showed them about 10 metres inside Mexico near the border city of Agua Prieta and the town of Douglas, Arizona.
The Mexican Foreign Minister Patricia Espinosa said she had complained to the US authorities and that the men and equipment had been withdrawn.
Continental trade concerns
In a statement, the US Ambassador to Mexico Tony Garza said: "The US is sensitive to Mexican concerns... [and] has the deepest respect for the integrity of the sovereignty of Mexican soil".
He said US Homeland Security Secretary Michael Chertoff had not been in the area of the alleged incursion and recent photographs of him welding a section of the fence had been taken in a different part of Arizona on the US side of the border.
The US says it is building 700 miles (1,125km) of fencing along its border with Mexico to stop illegal immigration.
Many Mexicans see the fence as offensive and say it will be ineffective and potentially cause more deaths in border crossings.
An estimated 1.2 million illegal immigrants were arrested in 2005 trying to cross into the US via the border states of Texas, New Mexico, Arizona and California.
About 11 million Mexicans are thought to live in the US, more than six million of them illegally.
Later on Friday, US Secretary of State Condoleezza Rice is meeting her Canadian and Mexican counterparts - Peter Mackay and Patricia Espinosa - in Ottawa.
They are to discuss concerns that security measures put in place after the 11 September 2001 attacks on the US may hamper trade between the three countries.
The officials will also look at co-ordinating responses to emergencies such as a pandemic outbreak of avian flu.