The United States has built what it's describing as a humanitarian and legal case for military action against Syria.
The US position is rooted in the proposition that an "undeniable" chemical attack has shattered international codes of war.
The growing likelihood of an international conflict comes as a United Nations team visiting Syria investigated the site of last week's alleged chemical attack.
Kerri Worthington reports.
"What we saw in Syria last week should shock the conscience of the world. It defies any code of morality. Let me be clear: the indiscriminate slaughter of civilians, the killing of women and children and innocent bystanders by chemical weapons is a moral obscenity. By any standard, it is inexcusable and despite the excuses and equivocations that some have manufactured, it is undeniable. Anyone who could claim that an attack of this staggering scale could be contrived or fabricated needs to check their conscience and their own moral compass."
US Secretary of State John Kerry's emotional indictment of the attack in Syria represents a swift change in tone from the US government.
Late last week, President Barack Obama was warning about the danger of new entanglements in a blood-soaked region, which may mire the US in very difficult situations.
But a combination of footage of dying children in a Damascus suburb last week, and what officials see as solid intelligence of government culpability, has shifted the US position since then.
According to US law, President Barack Obama has the authority to launch air strikes against Syria, but he has to notify Congress first.
John Kerry says the President will decide in the coming days what action to take.
"Our understanding of what has already happened in Syria is grounded in facts, informed by conscience, and guided by common sense. We have additional information about this attack and that information is being compiled and reviewed together with our partners and we will provide that information in the days ahead."
It's unclear exactly which international statutes the US administration will use to build its case, but the 1925 Geneva Protocol -- though never fully ratified -- provides a codified framework outlawing the use of poison gases in war.
But Russian Foreign Minister Sergei Lavrov is maintaining Russia's sceptical position over the claims the Syrian government was behind the attacks last week.
He has warned that intervening without a UN Security Council resolution would be illegal.
(with translation) "The hysteria is growing and confrontation is being incited based on the claim that the government of Syria has used chemical weapons on the 21st of August in Ghoutha. And, on this pretext, massive military buildup is being witnessed in the region. Washington, London and Paris have officially stated that they've cogent evidence, proof that that the Syrian regime is guilty but they can't present this evidence."
While a UN Security Council resolution authorising force would likely draw a Russian veto, the precedent for action by an international coalition without such a mandate was set by the 1990s Kosovo conflict.
Analysts say US military action in Syria would likely be constrained in scope -- probably starting with cruise missile strikes launched from US, and possibly allied ships and submarines.
Australian Prime Minister Kevin Rudd has made clear several times since the US Secretary of State's statements that Australia will stand with the US.
"As for the posture of the United States and the conversation I had with President Obama this morning, he is focused on the full range of options which he is in the process of discussing with his partners and allies around the world. We are an ally of the United States. I, like the President of the United States, am driven by a core imperative here, which is not allowing a message to be conveyed to the international community that the use of chemical weapons against anybody in the year 2013 is acceptable."
The United Nations is engaged in the process of gathering evidence of what happened in the apparent chemical attack, as well as other alleged incidents blamed on both sides of the Syrian conflict.
UN inspectors say they've gathered valuable evidence, even though their convoy was fired upon by unidentified attackers as it tried to approach Ghoutha, east of Damascus.
Kevin Rudd says what's happening in Syria is a crisis of historic proportions that can no longer be ignored.
"Our priority as Australia remains working with all corners of the world through our global diplomatic network to ensure (President) Assad allows full and unfettered access to UN inspectors. That has not been the case so far. The incident overnight where weapons were used and firing occurred against the first UN weapons vehicle is, I believe, a sobering reminder to the international community of what is at stake here."
Australia takes the rotating presidency of the United Nations Security Council on Sunday, and its diplomats will play a role in any UN-sanctioned action.
