Federal authorities rounded up more than 1,300 illegal immigrants in Southern California during the past two weeks in what officials said Wednesday was the largest sweep of its kind.

The raids targeted immigrants who had criminal records, defied final deportation orders or re-entered the U.S. illegally, according to the Immigration and Customs Enforcement agency.

About 90 percent of those taken into custody fell under those categories and included suspected street gang members.

"These aren't people that we want in our communities. These aren't just people looking for work," said Jim Hayes, director of the ICE office in Los Angeles.

Most of the immigrants were found at their homes, workplaces or jails.

Nearly 600 already have been returned to their native countries, officials said. Others will be prosecuted for illegal re-entry to the U.S. after felony deportations, a crime that can carry up to 20 years in prison.

The illegal immigrants arrested in the sweeps represented about 30 countries, though more than 1,100 were Mexican.

The operation by ICE fugitive operation teams resulted in 1,327 arrests, exceeding the 1,297 arrests the agency made last year in raids targeting meat processing plants in six states.

There are believed to be nearly 597,000 immigrant fugitives in the U.S., according to ICE.

In recent years, local authorities have worked with ICE to identify thousands of illegal immigrants in county jails. Those immigrants are handed over to ICE and placed in deportation proceedings after their criminal cases finish and they serve their prison sentences, Hayes said.