The number of undocumented Mexicans in the United States continues to fall, and between 2007 and 2010 the figure declined by about 400,000, mainly due to the harsher immigration policy in several states and high unemployment, Spanish banking giant BBVA said in a new report.

During the same period, U.S. Census Bureau figures show that the total number of Mexican immigrants remained constant at 11.8 million, the Spanish banking group, which has a service for immigration study in Mexico, said.

It is estimated that the number of documented Mexican immigrants who entered the United States "should also have increased by a similar figure (400,000 during the same years)" to compensate for the outflow of undocumented people, the bank said.

The report says that the number of Mexican immigrants decreased in states such as Arizona (by 13.2 percent between 2007 and 2010), Florida (41.4 percent), Georgia (21.6 percent), Alabama (37.3 percent and Tennessee (31.9 percent), in which anti-immigration laws have been implemented or are being discussed.

In contrast, in other states such as California, where the number of Mexican immigrants fell by 4.7 percent, as well as in Maryland (51.2 percent), Oregon (41.2 percent) and Arkansas (49.8 percent), "the high unemployment among Mexican migrants could be spurring their exit," the report said.

In general, Mexican migrants "are moving to states with low unemployment, or to states near those that have toughened their actions against immigrants like: Texas, New Jersey, Virginia, Washington and Michigan," BBVA said.

The poverty rate among Mexican immigrants is double that of the U.S. population in general, the report said.

The poverty rate registered "one of its greatest increases" by jumping from 22.1 percent to 29.8 percent between 2007 and 2011, a period during which about 1 million more Mexicans slid below the poverty line, bringing the total living in poverty to 3.5 million, BBVA said.