Mexico has sent a diplomatic note to the U.S. condemning a plan to build hundreds of kilometres of fencing along the border to block illegal immigrants.

In the letter to the U.S. State Department Monday, Mexico's Foreign Relations Department said only comprehensive reform could stem the tide of illegal immigrants looking for work in the U.S.

"The diplomatic note explains that the construction of this barrier will hurt the relations between the two countries and that it is not the solution to strengthen security on the border," the department said.

President-elect Felipe Calderon also criticized the plan, saying one  "could stop more migrants with a kilometre of new roads and development [in Mexico] than with a wall."

Mexican President Vicente Fox, who leaves office Dec. 1, has spent his six-year term lobbying for a new guest worker program and an amnesty for the millions of Mexicans working illegally in the U.S.

Last week, the U.S. Senate approved a bill authorizing more than 1,100 kilometres of new fencing in border states.

An estimated 11 million Mexican citizens are in the United States, about half of them illegally.

With files from the Associated Press