More than 100 facilities nationwide that store large amounts of lung-melting or other lethal chemicals are located near communities of at least 1 million people, congressional researchers say.

Officials are concerned that the plants, located in 23 states, are tempting targets for terror attacks.

The tally of plants was compiled by the Congressional Research Service (search), for release Wednesday, using Environmental Protection Agency (search) data. It represents one of the first public state-by-state breakdowns of how close potentially deadly facilities are located to the nation's largest population centers.

"Chemical facilities are at the top of the terrorists' target list, and I thought it would be helpful for the full picture to be presented," Rep. Edward J. Markey (search), D-Mass., said in an interview Tuesday.

The survey provided state-by-state figures but did not specify the names of the facilities or the cities in which they are located.

The EPA refuses to release its own list of detailed locations of the chemical manufacturing plants, oil refineries and storage facilities for fear doing so could aid terror plans. Environmental watchdog groups have compiled incomplete or outdated tallies of chemical facilities.

"Nobody wants us handing out information that people with nefarious things on their minds would use to their advantage," said EPA spokesman Dale Kemery.

Experts said the number of injuries or deaths caused by emissions of chemical explosives or toxic gases would depend largely on unpredictable factors like wind current or the extent of the leak. But they agreed the report highlights the continued danger of questionable security practices at plants.

If released, the toxic chemicals can "cause poison gas clouds to kill people," said Andy Igrejas, a chemical industry watchdog at the National Environmental Trust. "It's violent deaths you're talking about — it melts your lungs, essentially."

The report, completed at Markey's request, comes as the Homeland Security Department (search) considers tougher federal regulation of the chemical industry, which has largely policed its own security procedures.

Last month, Homeland Security Acting Undersecretary Robert Stephan told congressional committees that "it has become clear that the entirely voluntary efforts of these companies alone will not sufficiently address security for the entire sector."

Several industry representatives contacted Tuesday declined immediate comment.

The report estimates at least 106 and as many as 111 plants are located near population centers of 1 million people or more. Up to 29 of the plants were located in Texas — more than twice as many than in any other state.

Kemery, the EPA spokesman, and environmental experts agreed that the overall estimate represents a drop from 123 plants five years ago — partially because of industry efforts to use alternatives to the deadly chemicals or to move away from densely populated areas.