Free Syrian Army fighters sitting atop a tank that belonged to forces loyal to Syria's President Bashar al-Assad, hold up their weapons and cheer after seizing Aleppo's town of Khanasir August 26, 2013.[Photo/Agencies]

MOOD IN DAMASCUS

Syria's government, backed by Iran, denies gassing its own people and has vowed to defend itself, but residents of Damascus are growing anxious.

"I've always been a supporter of foreign intervention, but now that it seems like a reality, I've been worrying that my family could be hurt or killed," said a woman named Zaina, who opposes Assad. "I'm afraid of a military strike now."

"The big fear is that they'll make the same mistakes they made in Libya and Iraq," said Ziyad, a man in his 50s. "They'll hit civilian targets and then they'll cry that it was by mistake, but we'll get killed in the thousands."    

Russia, Assad's main arms supplier, opposes military action and has suggested that rebel forces may have released the poison gas. China's state news agency recalled how flawed intelligence was used to justify the US-led invasion of Iraq in 2003.

Firm opposition from permanent members of the UN Security Council all but rules out a UN mandate of the kind that gave legal backing to NATO air strikes that helped Libyan rebels unseat Muammar Gaddafi two years ago. However, Western officials say they do want to act within international law.

Moscow and Beijing accuse Western powers of using human rights complaints, such as in Libya, to meddle in sovereign states' affairs. White House spokesman Carney insisted: "The options that we are considering are not about regime change.

"They are about responding to a clear violation of an international standard that prohibits the use of chemical weapons." Although Obama has long said Assad should step down, he is unwilling to commit to making that happen by force. Carney said it was "profoundly in the interests of the United States" to respond to the chemical weapons attack.

In Britain, Cameron told reporters: "This is not about getting involved in a Middle Eastern war or changing our stance in Syria or going further into that conflict. It's about chemical weapons. Their use is wrong and the world shouldn't stand idly by."

In France, which played a major role in Libya, President Francois Hollande said he was "ready to punish" Assad for using the chemical weapons, citing a 2005 UN provision for international action to protect civilians from their own governments.

Similar arguments were used by NATO to bomb Serbia, a Russian ally, after the killing of civilians in Kosovo.

In an indication of support from Arab states that may help Western powers argue the case for an attack against likely UN vetoes from Moscow and Beijing, the Arab League issued a statement holding Assad's government responsible for the chemical attack.

Fears of another international conflict in the Middle East affected financial markets. Oil prices hit a six-month high and stocks fell around the world, notably in Turkey, as well as in emerging economies that would suffer from a chill in trade.

The government of Turkey, a NATO member, called for action against Assad for what it called a "crime against humanity."