An undated handout photo depicts UN weapons inspection led team prepares leaking rockets filled with Sarin for destruction in the Iraqi desert (Reuters)

Sarin gas is believe to have been used by the Syrian regime as a chemical weapon against its own people.

US President Obama had declared that the use of such weapons in the two-year civil war would be "game changer" that would cross a "red line" for a major military response, due to the devastating effects chemicals like sarin can cause.

Classified as a weapon of mass destruction by the UN, Sarin was originally developed in Nazi Germany as a pesticide in 1938. It is described as a "clear, colourless, and tasteless liquid that has no odour in its pure form," by the US Centres for Disease Control and Prevention (CDC).

"It is the most volatile of the nerve agents, which means that it can easily and quickly evaporate from a liquid into a vapour and spread into the environment."

In 1995 members of Japanese religious cult Aum Shinrikyo spread Sarin in the Tokyo underground, letting the liquid leak out of some punctured packets. 12 people were killed and more than 5,000 injured in the attack.

The gas was also used by Iraqi forces led by late dictator Saddam Hussein in the Iran-Iraq war in the 1980s.

Sarin was one of the chemicals allegedly used by Saddam Hussein in the infamous Halabja massacre against Kurdish population that left thousands dead in southern Kurdistan.

One breath of the nerve agent is enough to kill, but exposure might be caused also by skin and eye contact as well as ingestion by contamination of food and water.

Symptoms include: blurred vision, drooling, excessive sweating, cough, chest tightness, vomiting and confusion when exposed to a low or moderate dose of sarin and loss of consciousness ness, convulsions, paralysis and respiratory failure when exposed to a large amount of gas.

Yasser Yunis a 27-year-old car mechanic from Aleppo had is wife and sons killed by a chemical shell that hit his family house earlier this month.

Yunis told The Times he noticed a strange "sharp" tang in the air when he went to check the shell that had exploded in the stairwell as his family was sleeping at night.

"My wife and children were struggling to breath. Froth was coming from their mouths. The air had a strange sensation, sharp. My own throat began to constrict and my heart was hammering," Yunis told the British newspaper.

"My vision was going. I grabbed my boy Sadiq and ran for the street. Then I collapsed. I remember nothing more."

Sadiq, 18 months, died that night together with his wife Gadir Nadaf, 25 and the couple other son YahYah, 4 months.

Production and stockpiling of Sarin is banned under the Chemical Weapons Convention. Syria is one of the six world nation that is not to sign the treaty.

The others are North Korea, Somalia Egypt, South Sudan and Angola. Israel and Myanmar.