Nearly 200 illegal immigrants who were ordered deported for committing crimes were arrested during a six-day undercover sweep across New England (search), federal authorities said.

Dozens of federal, state and local law-enforcement officers began a search Friday for the roughly 200 people targeted in the sweep; by Wednesday afternoon, they had arrested at least 187 illegal immigrants.

Authorities planned a Thursday news conference to discuss the operation, believed to be the largest of its kind staged by an Immigration and Customs Enforcement (search) regional field office, said Bruce Chadbourne, ICE's New England field director.

Those arrested had served time in prison or jail for a wide range of crimes, including attempted murder, rape, child molestation and arson, authorities said.

Many illegal immigrants aren't immediately deported after serving time because local officials fail to notify federal authorities of the convicts' release.

"Some of them have gone through the criminal justice process, and we were not even aware of it," Chadbourne said. "(State prison officials) are not experts in immigration law. That's where we come in."

Last year, ICE arrested 10,982 of an estimated 500,000 illegal immigrants considered fugitives after they were ordered deported, according to Chadbourne.

The number of arrests could rise sharply this year: Homeland Security (search) officials recently announced plans to increase the number of ICE fugitive apprehension teams from 18 to 38 within the next two months, he said. Each team consists of roughly seven agents.