On Friday, Tony Garza, the US ambassador to Mexico, criticised statements by Mexican officials comparing the fence with the Berlin Wall and denied that the initiative violated the human rights of migrants trying to improve their lives.
Last month, the US House of Representatives approved a bill that would put up additional barriers along the US-Mexican border, a plan Vicente Fox, the president of Mexico, quickly opposed and compared with the Berlin Wall.
Garza said the bill would help enforce immigration laws and criticised Fox's historical allusion.
"Comparisons ... to the Berlin Wall are not only disingenuous and intellectually dishonest, they are personally offensive to me," Garza said in a news release.
"The Berlin Wall was built to keep its own people trapped inside, and was created by an oppressive authoritarian government."
The proposed law, which has yet to be passed by the US Senate, would make illegal migration a felony.
Thousands of people are thought to cross the 3200km Mexican-US border illegally every day, some risking their lives, in search of low-paying jobs in the United States.
"There is no human right to enter another country in violation of its laws," Garza said.
"More robust efforts by the Mexican government to create well-paying jobs for its citizens would dissuade many from making the dangerous and illegal crossing to the United States."
Fox's main foreign policy goal when he took office five years ago was to win sweeping US immigration reform in favour of millions of Mexicans living and working illegally in the United States.
But the two countries have drifted apart since the 11 September attacks as Washington focused more on its war on terrorism than on Latin America, and security fears along the US-Mexican border began to cause rifts.
"There is no human right to enter another country in violation of its laws"
Tony Garza, the US ambassador to Mexico
Bush has proposed a guest worker programme to offer an estimated 11 million illegal immigrants the chance to register and work for up to six years.
Many Republicans say Bush's proposal would reward lawbreakers and provide "backdoor amnesty".
The House has not yet taken up the guest worker proposal.