A team of United Nations chemical weapons experts have left Syria and crossed the border into Lebanon after two weeks taking samples from victims of the suspected chemical weapons attack.
Officials at the Damascus hotel where they were staying said the UN staff left early today and were believed to be on their way to Beirut.
Yesterday the team carried out a fourth and final day of inspections as they sought to determine precisely what happened in the alleged attack on August 21.
The samples will be examined in laboratories in Europe.
Their probe ended as US president Barack Obama said he was considering "limited and narrow" action against Syria. His administration bluntly accused Bashar Assad's regime of launching the attack that killed at least 1,429 people - far more than previous estimates - including more than 400 children.
But Mr Obama said there would be no "boots on the ground", seeking to reassure Americans weary after a decade of war in Iraq and Afghanistan.
With France his only major public ally, Mr Obama said he had a strong preference for multilateral action, adding: "Frankly, part of the challenge we end up with here is a lot of people think something should be done but nobody wants to do it."
French president Francois Hollande has endorsed punitive strikes but British prime minister David Cameron's attempt to win a vote of approval in Parliament for military action ended in ignominious defeat on Thursday night. And American attempts to secure backing at the United Nations have been blocked by Russia, long an ally of Syria.
UN secretary general Ban Ki-moon has urged a delay in any military action until the inspectors can present their findings to UN member states and the Security Council.
US warships were in place in the Mediterranean Sea, carrying cruise missiles, which can find a target hundreds of miles away without need of air cover or ground troops.
The Syrian government said the administration claims were "flagrant lies" akin to faulty Bush administration assertions before the Iraq invasion that Saddam Hussein had weapons of mass destruction.
A Foreign Ministry statement read on state TV said that "under the pretext of protecting the Syrian people, they are making a case for an aggression that will kill hundreds of innocent Syrian civilians".
People in Damascus have been stocking up on food and other necessities in anticipation of strikes.
Mr Obama met his national security aides at the White House and then diplomats from Baltic countries, saying he had not yet made a final decision on a response to the attack. But the administration did nothing to discourage the predictions that he would act - and soon.
It was an impression heightened both by strongly-worded remarks from secretary of state John Kerry and the release of an unclassified intelligence assessment that cited "high confidence" that the Syrian government carried out the attack.
In addition to the dead, the assessment reported that about 3,600 patients "displaying symptoms consistent with nerve agent exposure" were seen at Damascus-area hospitals after the attack.
To that, Mr Kerry added that "a senior regime official who knew about the attack confirmed that chemical weapons were used by the regime, reviewed the impact and actually was afraid they would be discovered". He added for emphasis: "We know this."
The assessment did not explain its unexpectedly large casualty count, far in excess of an estimate from Doctors Without Borders. Not surprisingly - given the nature of the disclosure - it also did not say expressly how the United States knew what one Syrian official had allegedly said to another.
Mr Kerry urged Americans to read the four-page assessment for themselves. He referred to Iraq - when Bush administration assurances that weapons of mass destruction were present proved false, and a US invasion led to a long, deadly war.
Mr Kerry said this time it would be different. "We will not repeat that moment," he said.
Citing an imperative to act, the nation's top diplomat said "it is directly related to our credibility and whether countries still believe the United States when it says something. They are watching to see if Syria can get away with it because then maybe they, too, can put the world at greater risk".
Mr Obama and Mr Hollande spoke by phone, then Mr Hollande issued a statement saying they had "agreed that the international community cannot tolerate the use of chemical weapons, that it must hold the Syrian regime responsible and send a strong message to denounce the use of (such) arms".
The looming confrontation is the latest outgrowth of a civil war in which Assad has tenaciously - and brutally - clung to power. An estimated 100,000 civilians have been killed in more than two years, many of them from attacks by the Syrian government on its own citizens.
Mr Obama has long been wary of US military involvement in the struggle, as he has been with turbulent events elsewhere during the so-called Arab Spring.
In this case, reluctance stems in part from recognition that while Assad has ties to Iran and the Lebanese militant group Hezbollah, the rebels seeking to topple him have connections with al Qaida terrorist groups.
But Mr Obama declared more than a year ago that the use of chemical weapons would amount to a "red line" that Assad should not cross. And Mr Obama approved the shipment of small weapons and ammunition to the Syrian rebels after an earlier reported chemical weapons attack, although there is little sign that the equipment has arrived.
Dozens of politicians, most of them Republican, have signed a letter saying Mr Obama should not take military action without congressional approval and leaders of both political parties are urging the president to consult more closely with congress before giving an order to launch hostilities.
But there has been little or no discussion about calling Congress back into session to debate the issue. Politicians have been on a summer break for nearly a month, and are not due to return until September 9.