REPUBLIKA.CO.ID, Charles Heyman, a former British officer who edits The Armed Forces of the UK, said the lack of a UN Security Council resolution authorizing the use of force against the Syrian government greatly complicates matters for the West. He said that may make it difficult for Cameron to win parliamentary backing.

"It's clear the governments want some form of military operation, but if the Security Council doesn't recommend it, then the consensus is that it's plainly illegal under international law," Heyman said. "The only legal way to go to war is in self-defense and that claim is difficult to make."

Heyman predicted a possible three-phase campaign, with the first step — the encirclement of Syria by Western military assets by air and sea — already underway.

"Phase two would be a punitive strike, taking out high-value command and control targets and communications centers," Heyman said. "That could be done easily with cruise missiles from ships and aircraft. Phase three would be a massive takedown of Syrian air defenses. That would have to be done before you could take out artillery and armor, which is the key to long-term success."

Meanwhile, support for some sort of international military response is likely to grow if it is confirmed that Assad's regime was responsible. The UN confirmed its chemical weapons team's mission faced a one-day delay Tuesday to improve preparedness and safety after unidentified snipers opened fire on the team's convoy Monday.

In Geneva, UN spokeswoman Alessandra Vellucci said the UN inspection team might need longer than the planned 14 days to complete its work. She said its goal is to determine what chemical weapons might have been used in the Aug. 21 attack.