But the most notorious sarin attack occurred in March 1988 in the village of Halabja in northern Iraq, when as many as 5000 Kurds were killed and 65,000 injured when the Iraqi military used a combination of chemical agents including sarin, mustard gas and possibly VX. 

Sarin killed 12 people and injured 5000 others when the Aum Supreme Truth cult released it on the Tokyo subway in March 1995. 

An artillery round containing the gas exploded after it was discovered by occupation forces in Iraq, causing a "very small dispersal of agent," a US military spokesman said on Monday. 

Former Iraqi leader Saddam Hussein's alleged possession of weapons of mass destruction was the main reason for the US-led invasion of Iraq more than a year ago, but no stockpiles have been found since the war.

Powerful

Sarin is considered 500 times more powerful than cyanide, used to kill millions in the gas chambers of Nazi death camps in the closing stages of World War II.

Saddam Hussein's regime began
producing sarin in 1984

Like other gases originally developed for war, sarin was never used on the battlefield. The fact that both Germany and the Allies had their own stockpiles of the deadly weapon proved a sufficient deterrent to its use.

First developed as an organophosphate pesticide, Sarin works by being inhaled or absorbed through the skin and kills by crippling the nervous system.

Symptoms include nausea and violent headaches, blurred or tunnel vision, drooling, muscular convulsions, respiratory arrest, loss of consciousness and then death, according to the US Centers for Disease Control and Prevention.

In high doses, sarin paralyses the muscles around the lungs and prevents chemicals from "switching off" the body's secretions, so victims suffocate or drown as their lungs fill with mucus and saliva.

Permanent effects

Even a tiny dose of sarin - which, like other nerve gases such as soman, tabun, and VX, is odourless, colourless, and tasteless - can be deadly if it enters the respiratory system, or if a drop comes into contact with the skin. 

In May 2002, the United States
accused Syria of having sarin

Even if it does not kill, sarin's effects can be permanent, inflicting lasting damage to the victim's lungs, eyes and central nervous system.

Being heavier than air, sarin can linger in an area for up to six hours, depending on weather conditions.

It is made from widely available chemicals including organic
phosphorous, sodium fluoride and alcohol, but specialist knowledge and apparatus are needed to make pure and long-lasting sarin.

Carbamates, a category of chemicals used in medicine and
insecticides, can increase human resistance to sarin and other nerve agents if taken before exposure. Another family of drugs, known as oximes, are also effective.

Drawn to Sarin

Some countries desperate to acquire weapons of mass destruction have been drawn to sarin and other poison gases, seeing in them a cheaper alternative to nuclear weapons.

Only Russia and the United States have officially declared that they have sarin stockpiles, but other countries - including Egypt, Iran, Libya, and North Korea - may also possess supplies, experts say.

In May 2002, the United States accused Syria of having sarin. Saddam Hussein's regime began producing sarin in 1984. In 1995 Iraq admitted to having produced 790 tons of it. Iraq is also suspected of using sarin against Iranian troops during the 1980s.