Syrian President Bashar al-Assad's regime and the
rebels fighting the government have accused each other of using
chemical weapons in the civil war, which is now in its 29th month. A
timeline of related events:
August 20, 2012: US President Barack Obama threatens a military strike if al-Assad's regime crosses a "red line" by using chemical weapons.
March 19, 2013: At least 30 killed when a rocket, reportedly containing chemicals, hits Khan al-Assal in the northern province of Aleppo. The government and rebels accuse each other of launching the attack.
April 8: Syria bars entry to a UN team that intends to check whether chemical weapons have been used in the civil war.
April 25: US intelligence agencies have indications the Syrian regime used chemical weapons. But there is still no clear evidence, Secretary of State John Kerry says.
May 6: Statements by UN expert Carla del Ponte that the rebels had used the poison gas sarin are met with scepticism in Washington. The independent UN commission on Syria states there is no proof.
May 18: Al-Assad says Western claims that his government used chemical weapons against its own people are a prelude to a war against Syria.
June 4: France says its tests confirm chemical weapons use; US government reacts cautiously to new incriminating reports by the UN Commission of Inquiry on Syria about the use of poison gas; White House says more evidence would need to be collected as to who was responsible for the likely use of chemical weapons and the circumstances under which this was done.
June 11: UN accepts an invitation by the Syrian government to investigate the alleged use of chemical weapons in Khan al-Assal.
June 14: US says its intelligence services have confirmed the use of chemical weapons by al-Assad's regime; announces that it will begin sending military assistance to the rebels.
July 9: Russia says its experts have collected samples of sarin nerve gas used by Syrian rebels in Khan al-Assal; provides an 80-page analysis to the UN, China, France, the United States and Britain.
July 24: Ake Sellstrom, the chief inspector for the UN investigative team, and Angela Kane, the UN high representative for disarmament, visit Syria to negotiate the terms of a possible investigation.
August 18: A 20-member UN team, led by Sellstrom, arrives in Damascus to investigate three sites of alleged chemical weapons attacks; one of sites is Khan al-Assal.
August 20: Syrian opposition activists accuse the regime of killing 635 people in "poisonous gas" attacks on rebel strongholds near Damascus; government says allegations are aimed at derailing UN mission.
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