WASHINGTON—As the last of the United Nations inspectors prepared to leave Syria, an ominous war window opened, with all signs in Washington pointing to imminent American airstrikes.

Nine days of international diplomatic anxiety over the uploaded scenes of Aug. 21, when more than 1,000 Syrian men, women and children died of apparent chemical asphyxiation, ended in a flurry of final preparations in Washington.

First, Secretary of State John Kerry all but pre-empted the UN, making the case to the American people — and by extension, the world — effectively declaring a war of morality on the regime of “thug and murderer” Bashar Assad.

With “high confidence,” said Kerry, the U.S. intelligence holds Syria’s president responsible for unleashing chemical hell on a dozen targets in the outskirts of Damascus, killing at least 1,429 people, including 426 children.

Read the full U.S. government report on Syria (pdf)

“This is evidence. These are facts,” said Kerry, stressing that with American credibility on the line, the White House was steeling for a military response, even with the sudden withdrawal of longtime ally Britain from the equation.

“It is about Hezbollah and North Korea and every other terrorist group or dictator that might ever again contemplate the use of weapons of mass destruction,” Kerry said.

“And because of the guaranteed Russian obstructionism of any action through the UN Security Council, the UN cannot galvanize the world to act, as it should.”

As Kerry spoke, the White House declassified a long-awaited dossier backing the claims, together with a map showing the locations of the strikes.

“We know what the doctors and the nurses who treated them didn’t report,” Kerry said of the victims. “Not a scratch. Not a shrapnel wound. Not a cut. Not a gunshot wound. We saw rows of dead lined up in burial shrouds, the white linen unstained by a single drop of blood.”

President Barack Obama, the ultimate arbiter on retaliatory strikes that new polls suggest barely one in five Americans favour, insisted in brief comments Friday that no final decision has been taken.

Obama lamented the results of aggressive U.S. efforts to build a broad coalition for military response, saying: “A lot of people think something should be done but nobody wants to do it.”

With that, the buildup gave way to a tense countdown, as official Washington exited into the Labour Day long weekend on war footing. With all its military pieces in place, including destroyers, submarines and air assets, and U.S. media reports of as many as 50 Syrian targets identified, one final, seemingly innocuous White House email arrived at 6:20 p.m. Friday.

“On Saturday, Sunday and Monday, the President has no public events scheduled,” the White House missive read.

There was a sense of finality on the Syrian end. One final retort from the Assad regime, denying all and ridiculing Kerry’s claims as “fabricated” narratives circulated by the fragmented opposition.

“The Foreign Ministry is surprised that a great country is deceiving its public opinion in such a naïve way through relying on ‘no evidence,’ ” the Syrian statement said. “The United States adopts its stances in war and peace over what is being circulated on social networking sites.”

But behind the brinksmanship were a series of alarming, unconfirmed reports out of Damascus suggesting a flurry of activity, including the movement of troops and other military assets into densely populated civilian areas of the capital. Opposition sources also claimed that Syrian rebel prisoners had been locked inside numerous military installations, raising fears that any U.S.-led assault could result in unintended casualties even if the missiles hit their marks.

Making the case for morality, Kerry avoided the case for legality — and whether the United States alone has the legitimacy to act unilaterally on the world’s behalf.

But as the day unfolded, it became clear that while lonely on the question of imminent action in Syria, the U.S. is not entirely alone. Kerry declared himself “confident and gratified” that its “oldest ally,” France, was committed to the mission, together with Australia and Turkey.

He made no mention of Britain, where the aftermath of a stunning Thursday night parliamentary vote rejecting Prime Minister David Cameron’s bid for U.K. participation continued to reverberate.

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Canada, for its part, renewed its symbolic support Friday in a statement from Foreign Affairs Minister John Baird that left no doubt Ottawa would remain observers, not participants.

“Although the Prime Minister made very clear yesterday that the government of Canada has no plans at this time for a Canadian military mission, we fully support our friends and allies in responding to the Assad regime’s horrific attack on its own people,” Baird said.

“The Obama administration has shown great resolve and proper due diligence in the past week, and we fully support its efforts going forward.”

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