Latino convicts now represent the largest ethnic population in the federal prison system, accounting for 40 percent of those convicted of federal crimes, according to a study released Wednesday by the Pew Research Center, a nonpartisan research organization.

Latinos made up only 13 percent of the United States adult population in 2007, but they accounted for one third of federal prison inmates that year, a result the study attributed to the sharp rise in illegal immigration and tougher enforcement of immigration laws.

Nearly half of Latino offenders, or about 48 percent, were convicted of immigration crimes, while drug offenses were the second-most-prevalent charge, according to the report.

As the annual number of federal offenders more than doubled from 1991 to 2007, the number of Latino offenders sentenced in a given year nearly quadrupled, to 29,281 from 7,924.