Undercover NYPD investigators secretly set up a fake water-purification company last year to demonstrate how easily and anonymously a terrorist could purchase toxic chlorine on the Internet for a deadly chemical strike against the city.

A videotape — showed at a counterterrorism briefing for private security executives on Wednesday — discusses the threat and for the first time discloses the results of "Operation Green Cloud" — a reference to the yellow-green color of chlorine gas.

The purpose was "to assess the ease or difficulty with which a terrorist in the United States could acquire large quantities of chlorine without being detected by law enforcement or intelligence agencies," a narrator says on a copy of the video obtained by The Associated Press.

The conclusion: "At the present time, few if any barriers stand in his way."

There has been no specific terror threat against the city involving chemicals, but the NYPD recently put more emphasis on screening shipments of chlorine after learning that it has become a favored component of homemade bombs in Iraq. A 2007 United Nations report found that at least 10 attacks there involved explosives attached to chlorine canisters.

Police Commissioner Raymond Kelly said that while there were no places to obtain chlorine in New York, there are several locations in neighboring New Jersey.

"It's something we have to be concerned about," he said of the potential of an attack using chlorine. "We think the whole area needs a lot of regulation."

Chlorine typically is used as a disinfectant or purifier, and as an ingredient in plastics and other products. While routinely transported in liquid form, it can turn into a deadly toxic gas when exposed to air.

Kelly said that the NYPD has been lobbying the Department of Homeland Security to draft stricter regulations requiring chlorine vendors to verify the legitimacy of their customers.

The department sent federal officials a copy of the videotape and "asked them to include strict 'know-your-customer' rules," Kelly said.

Police stressed that the chlorine deal was within current regulations, which have no requirement that vendors verify identification of their customers or report transactions.

In the video, an intelligence detective describes how in June 2007 the department fabricated a construction firm, complete with a mailing address, Web site and a phony contract with the city to clean up a polluted creek in Brooklyn. Investigators, after using the Internet to identify local vendors, used a credit card to place an order with one unnamed firm for three 100-pound cylinders of chlorine.

No one ever asked for identification and the purchase required little human interaction, police said.

The video includes surveillance footage of a truck delivering the canisters on a rain-slicked Brooklyn street lined with warehouses. At the time, hazardous material teams were on standby to respond to any accidents, police said.

The surveillance shows the truck driver and an undercover officer posing as the customer exchanging friendly banter as the delivery is made.

The driver "never asked for identification, he just asked for my name," the undercover officer says on the video. "I didn't feel he was uncomfortable or had any kind of concern."

In 2007, terrorists launched a spate of chlorine attacks in Iraq. That prompted a stern statement from the Defense Department in March, in which officials said such methods were akin to the mustard gas attacks that Saddam Hussein carried out in the 1980s.

In May, a suicide bomber exploded a tanker truck near an Iraqi police checkpoint outside a market west of Baghdad, killing at least two officers and injuring nine people. Police said they suspected chlorine gas was used in the attack.

And in October, Iraqi security forces arrested a suspected al-Qaida member in Iraq in a raid that also netted a cache of 60 roadside bombs and 89 pounds of chlorine powder.