Hundreds of Mexicans marched through Mexico City Monday to support illegal immigrants demonstrating for more rights in the United States and to boycott U.S. businesses.

The protests on May Day coincided with rallies throughout the United States, where hundreds of thousands of people took to the streets for what was called "A Day Without Immigrants."

Mexican President Vicente Fox, who has pushed hard for U.S. immigration reform, urged Mexicans taking part in the rallies to be prudent. He said they should not be an element of provocation or one that promotes xenophobia or opposition to immigration reform.

The Washington-based Pew Hispanic Center said in a recent report that the number of undocumented migrants in the United States has tripled over the past 20 years, despite efforts to limit illegal immigration.

The research organization said Latin Americans comprise 78 percent of the undocumented population, with 56 percent coming from Mexico.

The center said that from 2000 to 2005, the number of unauthorized Mexican migrants grew by about 1.5 million people. It said undocumented workers account for nearly five percent of the civilian work force.