The Arab League squarely blamed Syrian President Bashar Assad on Tuesday for a gas attack near Damascus and urged the UN Security Council to act, providing what diplomatic sources said was political cover for a possible US strike.
Western powers have told the Syrian opposition to expect a strike against Assad's forces within days to punish the attack, according to sources who attended a meeting between envoys and the Syrian National Coalition.
The Arab League's statement, issued after an emergency meeting, made no mention of military action. But it accused Assad of genocide and demanded, in unusually strong language, that the perpetrators of last week's poison gas attack, in which hundreds of civilians were killed, face justice.
The Arab League holds Syria "fully responsible for the ugly crime and demands that all the perpetrators of this heinous crime be presented for international trials", the statement said.
It also called on UN Security Council members to overcome their differences and take "the necessary resolutions against the perpetrators of this crime".
Russia and China have vetoed measures against Assad in the Council over the past two years. Russia in particular argued that Western powers abused a resolution in 2011 to justify military action to help topple Libyan leader Muammar Gaddafi - action that was endorsed by the Arab League.
Diplomatic sources said the Arab League statement had been pushed through by the Gulf states, particularly Saudi Arabia and Qatar, in the knowledge that air strikes were being discussed.
The two countries have been among the most ardent backers of Syria's rebels and have pressed for firmer action against Assad.
Saudi Foreign Minister Saud al-Faisal urged the international community on Tuesday to take a "serious and decisive" stand against the Syrian leader.
Syria's civil war has split the region broadly along sectarian lines. Shi'ite Muslim Iran, and its allies in Lebanon and Iraq, have supported Assad. The Gulf Arab states have backed the mainly Sunni Muslim rebels, many of whom are Islamist militants.
Iraq and Lebanon, as well as Algeria, withheld their backing for the Arab League statement or parts of it on Tuesday, as they have done in the past.