Syria acknowledged this week for the first time that it possesses chemical weapons, and threatened to use them if the country came under foreign attack. President Bashar Assad's regime is believed to have mustard gas as well as nerve agents such as tabun, sarin and VX. Here's a look at some of the chemical weapons believed to be in Syria's arsenal, how they work and when they have been used:
_ MUSTARD GAS
One of the best known chemical weapons, mustard gas is a blister agent that attacks the eyes and skin, causing severe blisters. If inhaled, it can also damage the lungs and other organs. The gas does not cause immediate symptoms, which means those exposed to it can unknowingly induce high dosages. While not usually lethal, exposure to mustard gas is generally debilitating.
Mustard gas was first used by the German army in World War I against British forces. Saddam Hussein was accused of using the gas in Iraq's eight-year war with Iran in the 1980s, as well as in his 1987-1988 crackdown on the country's Kurdish minority. The most notorious case was on the village of Halabja, which killed some 5,000 people in the deadliest chemical weapons attack ever against civilians.
_ NERVE AGENTS
The most toxic of the chemical weapons, nerve agents affect the nervous system and are hazardous in their liquid and gas states. They can be delivered in missiles, bombs, rockets, artillery shells and other large munitions.
The Syrian regime is believed to possess tabun, sarin and VX. Induced through the skin or by inhaling, these agents can – within seconds or minutes of exposure depending on the dose – cause extreme runny nose and salivation, blurred vision, nausea, vomiting, diarrhea and convulsions. Death is generally caused by paralysis of the respiratory system, which causes the victim to suffocate.
The first nerve agents were developed in Germany before and during World War II, although the Nazis did not use them during the war. The only time nerve agents are believed to have been used on the battlefield was in the Iraq-Iran war.