People who immigrated to the United States illegally are responsible for an increase in gang violence in Frederick County, Maryland, the county's sheriff said Tuesday at a congressional hearing on immigration reform.

Sheriff Charles Jenkins said before the House Subcommittee on Immigration and Border Security that immigrants in the U.S. illegally are committing crimes in the county and recruiting in local schools.

"Some of the problems that have started in the communities with the gang presence is now spreading into our high schools -- some of it into our middle schools. [At] one of the local high schools, routinely [there are] fights between rival gangs," he said, referring to Frederick High School.

Jenkins said more than 75 gang members are active in Frederick County. The sheriff said he believes the 18th Street Gang and MS-13 are recruiting in schools.

Gang activity is not a problem limited to schools, Frederick County Public Schools spokesman Michael Doerrer said.

"To the extent that gangs are an issue in Frederick County, they are a community issue, not a school system issue per se," he said.

Jenkins is known for hard-line policies on immigration. Frederick County deputies perform an immigration background check on everyone they arrest.

"We have placed 1,400 individuals who were in this country illegally and committed crimes in our county -- [they] have been placed in removal proceedings," he said.

Eighteen gang members arrested in the county since 2014 were charged with felonies, including an unprovoked assault on a deputy and a gang member involved in a hired killing, Jenkins said.

Some members of Frederick's growing Latino community challenged Jenkins' statements.

"Gang violence has existed among every race [and] not just illegals," Crystal Trejo said. "He's just trying to find somewhere to place the blame."