Mexico's government has lodged an official protest with the United States, after a U.S. Border Patrol agent shot dead an illegal migrant last week.

The man was killed during a confrontation with the Border Patrol agent when he was caught illegally crossing into the southern U.S. state of Arizona, along with six other migrants.

In the diplomatic note sent to Washington, Mexico said it is seriously concerned by such incidents. It also called on the United States to conduct a thorough investigation of the shooting and to punish those responsible.

The U.S. government has tightened security along its border with Mexico by deploying National Guard troops to back up Border Patrol units.

Last October, President Bush signed a controversial bill authorizing a new fence along the border.

Some information for this report was provided by AP and Reuters.