For a few thousand dollars, Chinese companies offer to export a powerful chemical that has been killing unsuspecting drug users and is so lethal that it presents a potential terrorism threat, an Associated Press investigation has found.

The AP identified 12 Chinese businesses that said they would export the chemical — a synthetic opioid known as carfentanil — to the United States, Canada, the United Kingdom, France, Germany, Belgium and Australia for as little as $2,750 US a kilogram, no questions asked.

Carfentanil is the latest scourge in an epidemic of opioid abuse that has killed tens of thousands of people in the United States alone. Dealers have been cutting carfentanil and its weaker cousin, fentanyl, into heroin and other illicit drugs to boost profit margins.

Despite the dangers, carfentanil is not a controlled substance in China, where it is manufactured legally and sold openly online. The U.S. government is pressing China to blacklist carfentanil, but Beijing has yet to act, leaving a substance whose lethal qualities have been compared with nerve gas to flow into foreign markets unabated.

"We can supply carfentanil, for sure," a saleswoman from Jilin Tely Import and Export Co. wrote in broken English in a September email. "And it's one of our hot sales product."

China's Ministry of Public Security declined multiple requests for comment from the AP.

This June 2016 photo provided by the RCMP shows printer ink bottles containing carfentanil imported from China, in Vancouver. (RCMP via AP)

Before being discovered by drug dealers, carfentanil and substances like it were viewed as chemical weapons. One of the most powerful opioids in circulation, carfentanil is so deadly that an amount smaller than a poppy seed can kill a person. Fentanyl is up to 50 times stronger than heroin; carfentanil is chemically similar, but 100 times stronger than fentanyl itself.

"It's a weapon," said Andrew Weber, assistant secretary of defense for nuclear, chemical and biological defence programs from 2009 to 2014. "Companies shouldn't be just sending it to anybody."

Canadian package labelled as printer cartridges

The AP did not actually order any drugs so could not conduct tests to determine whether the products on offer were genuine. But a kilogram of carfentanil shipped from China was recently seized in Canada.

The carfentanil shipped from China was in a box labelled printer accessories.

The powder contained 50 million lethal doses, according to the Canada Border Services Agency — more than enough to wipe out the entire population of the country. It was hidden inside bright blue cartridges labelled as ink for HP LaserJet printers. "Keep out of reach of children," read the labels, in Chinese.

Royal Canadian Mounted Police officers in Vancouver sealed themselves inside hazmat suits, binding their wrists, ankles, zippers, and face masks with fat yellow tape. With large oxygen containers on their backs and chunky respirators, it looked as if they were preparing for a trip to the moon.

"Cocaine or heroin, we know what the purpose is," said Allan Lai, an officer-in-charge at the Royal Canadian Mounted Police in Calgary, who is helping oversee the criminal investigation. "With respect to carfentanil, we don't know why a substance of that potency is coming into our country."

U.S. fentanyl seizures skyrocket

Carfentanil was first developed in the 1970s in Belgium, and its only routine use is as an anesthetic for elephants and other large animals. Governments quickly targeted it as a potential chemical weapon. Forms of fentanyl are suspected in at least one known assassination attempt, and were used by Russian forces against Chechen separatists who took hundreds of hostages at a Moscow theater in 2002.

The chemicals are banned from the battlefield under the Chemical Weapons Convention.

In fiscal year 2014, U.S. authorities seized just 3.7 kilograms of fentanyl. This fiscal year, through just mid-July, they have seized 134.1 kilograms, according to U.S. Customs and Border Protection data obtained by the AP. Fentanyl is the most frequently seized synthetic opioid, U.S. Customs reports.

Xu Liqun, centre, president of Hangzhou Reward Technology, speaks at the company's booth during the China International Chemical Industry Fair in Shanghai on Sept. 21. Liqun said her company could produce carfentanil to order. (Andy Wong/The Associated Press)

Users are dying of accidental respiratory arrest, and overdose rates have soared. China has not been blind to the key role its chemists play in the global opioid supply chain. Most synthetic drugs that end up in the United In States come from China, either directly or by way of Mexico, according to the DEA. China already has placed controls on 19 fentanyl-related compounds. Adding carfentanil to that list is likely to only diminish, not eliminate, global supply.

Despite periodic crackdowns, people willing to skirt the law are easy to find in China's vast, freewheeling chemicals industry, made up of an estimated 160,000 companies operating legally and illegally. Vendors said they lie on customs forms, guaranteed delivery to countries where carfentanil is banned and volunteered strategic advice on sneaking packages past law enforcement.

Speaking from a bright booth at a chemicals industry conference in Shanghai last month, Xu Liqun said her company, Hangzhou Reward Technology, could produce carfentanil to order.

"It's dangerous, dangerous, but if we send 1kg, 2kg, it's OK," she said, adding that she wouldn't do the synthesis herself because she's pregnant. She said she knows carfentanil can kill and believes it should be a controlled substance in China.

"The government should impose very serious limits, but in reality in China it's so difficult to control because if I produce one or two kilograms, how will anyone know?" she said. "They cannot control you, so many products, so many labs."

Several vendors recommended sending the drugs via EMS, the express mail service of state-owned China Postal Express & Logistics Co., as a fail-safe option.

EMS declined to comment.

Used in Chechen massacre response

Not all of the websites used to sell the drugs are based in China. At least six Chinese companies offering versions of fentanyl, including carfentanil, had IP addresses in the United States, hosted at U.S. commercial web providers, the AP found.

In this early Saturday, Oct. 26, 2002 file photo, unconscious liberated hostages are taken away in a bus from the scene near the Dubrovka Theater in Moscow. Russian special forces turned to carfentanil to end a standoff with Chechen separatists using an aerosol version of the opioid. (Dmitry Lovetsky/The Associated Press) In 2002, Russian Special Forces turned to carfentanil after a three-day standoff with Chechen separatists, who had taken more than 800 people hostage in a Moscow theatre. They used an aerosol version of carfentanil, along with the less potent remifentanil, sending it through air vents, according to a paper by British scientists who tested clothing and urine samples from three survivors.

The strategy worked, but more than 120 hostages died from the effects of the chemicals.

Olga Dolotova, an engineer who survived the attack, remembers seeing white plumes descending before she lost consciousness. When she awoke, she found herself on a bus packed with bodies. "It was such a horror just to look at it," she said. "Nobody was moving. They put the people there like dolls."

The theatre siege raised concerns about carfentanil as a tool of war or terrorism, and prompted the U.S. to develop strategies to counter its use, according to Weber, the former Defense Department chemical weapons expert.

"Countries that we are concerned about were interested in using it for offensive purposes," Weber said. "We are also concerned that groups like ISIS could order it commercially."

Weber considered a range of alarming scenarios, including the use of carfentanil to knock out and take troops hostage, or to kill civilians in a closed environment like a train station. He added that it is important to raise awareness about the threat from carfentanil trafficking.

"Shining sunlight on this black market activity should encourage Chinese authorities to shut it down," he said.

This combination of images from a 1997 report by the Lawrence Livermore National Laboratory shows photos from the testing of fentanyl-based anesthetics delivered via felt projectiles. The U.S. began researching fentanyl as an incapacitating agent in the 1960s. (Lawrence Livermore National Laboratory via AP) Fentanyls also have been described as ideal tools for assassination — lethal and metabolized quickly so they leave little trace.

The U.S. began researching fentanyl as an incapacitating agent in the 1960s and, by the 1980s, government scientists were experimenting with aerosolized carfentanil on primates, according to Neil Davison, the author of Non-Lethal Weapons who now works at the International Committee of the Red Cross.

Among the problems with fentanyls is that the line between life and death is too thin.

"There is no incapacitating chemical agent that can be used in a tactical situation without extreme risk of injury or death to everybody in the room," Crowley said.

DEA officials say they are getting unprecedented cooperation from China in the fight against fentanyls, noting unusually deep information sharing in what can be a fractious bilateral relationship.

Not yet on China's banned list

The DEA has "shared intelligence and scientific data" with Chinese authorities about controlling carfentanil, according to Russell Baer, a DEA special agent in Washington.

"I know China is looking at it very closely," he said. "That's been the subject of discussion in some of these high-level meetings."

Last October, China added 116 synthetic drugs to its controlled substances list, which had a profound impact on global narcotics supply chains. Acetylfentanyl, for example, is a weaker cousin of carfentanil that China included on last year's list of restricted substances. Six months later, monthly seizures of acetylfentanyl in the U.S. had plummeted by 60 percent, DEA data obtained by the AP shows.

Several vendors contacted in September were willing to export carfentanil, but refused to ship the far less potent acetylfentanyl. A Jilin Tely Import & Export Co. saleswoman offered carfentanil for $3,800 a kilogram, but wrote, with an apologetic happy face, that she couldn't ship acetylfentanyl because it "is regulated by the government now."

In August and September, high-level delegations of Chinese and U.S. drug enforcement authorities met to discuss joint efforts on synthetic opioids, but neither meeting produced any substantive announcement on carfentanil.

Nonetheless, some Chinese vendors are already bracing for a new wave of controls. In an email, Wonder Synthesis wrote, "If you need any chems, just hurry to buy."