President Barack Obama insisted Friday that war weariness cannot excuse world powers from their duty to punish Syria after the gassing to death of hundreds of women and children.
While he said he had made no "final decision" on taking military action against Bashar al-Assad's regime, Obama gave his clearest indication yet that a "narrow, limited" attack is imminent.
His remarks came after the United States released an intelligence report that concluded the regime had launched a chemical onslaught in the suburbs of Damascus last week, killing 1,429 people, including at least 426 children.
"This kind of attack is a challenge to the world," Obama told reporters at the White House.
"We cannot accept a world where women and children and innocent civilians are gassed on a terrible scale," he said, calling the attack a threat to US "national security interests."
"The world has an obligation to make sure we maintain the norm against the use of chemical weapons," he said, slamming the failure of the UN Security Council to agree on action.
Obama said he was looking at a "wide range of options" but had ruled out "boots on the ground" or a "long-term campaign."
"We are looking at the possibility of a limited, narrow act," he said.
France gave its backing to the US plans, saying a "strong message" should be sent to the Assad regime, but British lawmakers had already voted against any involvement in military action and other close US allies said they would not sign up.
Russia, Syria's most powerful ally, has questioned US intelligence about the August 21 gas attacks and has warned against any military strikes without UN backing.
In Damascus, UN experts completed their investigation into the attacks east of the capital and said they would "expedite" a report on whether chemical weapons had been used there.
The team is due to leave the war-battered country Saturday and report back immediately to UN chief Ban Ki-moon, who has appealed to the West to allow time for their findings to be assessed.
US Secretary of State John Kerry cited "multiple streams of intelligence" indicating that the Syrian government had carried out the chemical attack and that Assad himself is the "ultimate decision maker."
Kerry said failure to act would not only erode the nearly century-old norm against the use of chemical weapons, but would embolden Syrian allies Iran and Hezbollah.
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But the United States, faced with an impasse at the Security Council and the British parliament's shock vote Thursday, has been forced to look elsewhere for international partners.
While Germany and Canada ruled out joining any military strikes, French President Francois Hollande -- whose country was a strident opponent of the US-led war on Iraq -- said the British decision would not affect his government's stance.
Hollande said he and Obama "agreed that the international community cannot tolerate the use of chemical weapons, that it should hold the Syrian regime accountable for it and send a strong message."
Turkey, Syria's neighbor, went further still, demanding not just surgical strikes to send a message about chemical weapons but a sustained campaign to topple the regime.
"A limited operation cannot be satisfactory for us," Recep Tayyip Erdogan was quoted as saying by the NTV news channel.
Gruesome pictures of some of the reported victims of the attacks, including children, have shocked the world and piled on the pressure for a response that could draw a reluctant West into the vicious Syrian civil war.
But Russia and Iran, and even some US allies, have warned against any intervention, saying it risks sparking a wider conflict.
Divisions over Syria have further chilled the frosty relations between Washington and Moscow ahead of the G20 summit next week in Saint Petersburg, where pointedly there will be no face-to-face talks between Obama and Russian President Vladimir Putin.
Syria has denied using chemical weapons, and the foreign ministry said Friday that the US intelligence report was "nothing but tired legends that the terrorists have been circulating for more than a week, with their share of lies and entirely fabricated stories."
The military buildup was meanwhile continuing, with US warships armed with scores of cruise missiles converging on the eastern Mediterranean.
In Damascus the mood was heavy with fear and security forces were making preparations for possible air bombardments, pulling soldiers back from potential targets.
More than 100,000 people have died since the conflict erupted in March 2011 and two million have become refugees, half of them children, according to the United Nations.
Some commentators have questioned the wisdom of Obama dragging the United States into another conflict after the wars in Iraq and Afghanistan -- particularly as Al-Qaeda militants are among the rebels fighting the Assad regime.
Some members of the US Congress have voiced support for limited missile strikes, while urging transparency from the administration.
But an opinion poll released Friday said half of all Americans believe Obama should not intervene.