CHICAGO – Participants in an international Internet chat room transmitted live visuals of child molestation and traded thousands of pictures of child pornography, federal authorities said yesterday in announcing charges against 27 people.

American and international authorities have charged 27 people who took part in the Kiddypics & Kiddyvids chat room. The youngest child seen in pictures or video was less than 18 months old, Attorney General Gonzales said in announcing the results of the 10-month investigation.

The defendants include Brian Annoreno of Chicago, who prosecutors say molested an infant and transmitted it live to a viewer in the Canadian city of Edmonton.

“The behavior in the chat room and the images sent around the world … are the worst imaginable form of child pornography,” Mr. Gonzales said at a news conference in Chicago.

Investigators identified seven children who were molested on the streaming video, Mr. Gonzales said. Four molesters are among those charged, prosecutors said.

Thirteen people have been indicted in nine states on charges that include possession, receipt, distribution, and manufacture of child pornography. The states are: Arizona, Florida, Hawaii, Illinois, Michigan, Nevada, New York, North Carolina, and Tennessee.

The other 14 have been charged in Australia, Canada, and Britain. One person remains at large. The investigation began with an arrest in Edmonton last May.

U.S. Immigration and Customs Enforcement, a unit of the Homeland Security Department, led the American investigation.

Undercover agents gained entry to the chat room and identified the 27 people, initially through their screen names, officials said.

DHS Assistant Secretary Julie Myers said investigators told her this case was among the worst they’ve seen. “It’s hard to find cases more heinous than those that involve child molestation,” Ms. Myers said.

Mr. Gonzales has made crimes against children and online pornography top priorities for the Justice Department.

Also Wednesday, the Justice Department said it has quadrupled prosecutions of human trafficking crimes when comparing the first five years of the Bush administration with the last five years of the Clinton administration.

There were 91 cases in which people were accused of forcing women and children to work in sweatshops or prostitution between 2001 and 2005, the department said in a new report.