The United States is warning there are signs that Syria might be assembling chemical weapons, including sarin gas. Sarin is among the deadliest chemical weapons - capable of quickly sickening and killing thousands of a people across a wide area.
The conflict between rebels and the Syrian government is intensifying. Now U.S. officials say there is "movement activity" around Syria’s chemical weapons sites.
Experts say it is a dangerous sign that a war involving weapons of mass destruction might be about to begin.
Tim Brown is a security analyst with Globalsecurity.org. He says sarin gas is among the most lethal weapons in existence.
“Unless you’re in a full body suit and have a fully sealed gas mask, two to three parts per million will kill you. It’s a nerve agent," said Brown.
The threat of sarin gas is not new.
Members of a cult used it in a Tokyo subway attack that killed 13 people in 1995.
Iraq, under Saddam Hussein, possessed it in its arsenal of weapons of mass destruction.
Saddam's use of other types of poison gas against Iranian troops in the Iran-Iraq War and against Iraq's Kurdish population in the 1980s was criticized by the international community, but there were no threats of military action against Baghdad by the United States and its allies at the time.
Analyst Tim Brown says the international community has evolved.
“The U.S. and the West are powers that decided that the use of chemical weapons - the use, period - is not going to be tolerated," he said.
That was clear in 2003 when the United States went to war with Iraq on the belief that it still possessed weapons of mass destruction.
Now the United States has warned Syrian President Bashar al-Assad against the use of poison gas.
"I want to make it absolutely clear to Assad and those under his command, the world is watching. The use of chemical weapons is and would be totally unacceptable and if you make the tragic mistake of using these weapons, there will be consequences and you will be held accountable," said President Obama.
Details of what those consequences would be have not been made public. But analysts say a first step might be an air campaign to disable Syria’s air defense system and other means of delivering chemical weapons that could threaten its own population or neighboring countries such as Israel.