BEIRUT People in Damascus stocked up on supplies on Wednesday and some left homes close to potential targets as U.S. officials sketched out plans for multi-national air strikes on Syria that could last for days.
U.N. chemical weapons experts completed a second field trip to rebel-held suburbs, looking for evidence of what caused an apparent poison gas attack that residents say killed hundreds of people a week ago.
But as U.N. chief Ban Ki-moon appealed for unity among world powers and sought more time for the inspectors to complete their work, Washington and its European and Middle East allies said their minds were made up and that President Bashar al-Assad must face retribution for using banned weapons against his people.
There were growing signs, however, that the timeline for launching a widely expected military strike on Syria could be complicated not only by the U.N. inspectors' continued presence there but by the Obama administration's efforts to coordinate with international partners and growing demands for consultation with U.S. lawmakers.
Syria's government, supported notably by its main arms supplier Russia, cried foul. It blamed rebel "terrorists" for releasing the toxins with the help of the United States, Britain and France, and warned it would be a "graveyard of invaders".
Syrian officials say the West is playing into the hands of its al Qaeda enemies. The presence of Islamist militants among the rebels has deterred Western powers from arming Assad's foes. But the West says it must now act to stop the use of poison gas.
Britain pushed the other four veto-holding members of the U.N. Security Council at a meeting in New York to authorise military action against Assad to protect Syrian civilians - a move certain to be blocked by Russia and, probably, China. The meeting ended without a decision.
The United States and its allies say a U.N. veto will not stop them. Western diplomats called the proposed resolution a manoeuvre to isolate Moscow and rally a coalition behind air strikes. Arab states, NATO and Turkey also condemned Assad.
Washington has said repeatedly that President Barack Obama has not yet made up his mind on what action he will order.
A senior U.S. official said strikes could last several days and would involve other armed forces: "We're talking to a number of different allies regarding participation in a possible kinetic strike," the official said on Wednesday.
Western armies are expected to wait until the U.N. experts withdraw. Their initial 14-day mandate expires in four days, and Ban said they needed four days to complete the work.
A second U.S. official said objectives were still being defined but that the targets could be chosen to prevent Assad from using chemical weapons in future. Washington was confident it could handle Syrian defences and any possible reprisals by its allies, including Iran and Lebanese militia Hezbollah.
INVESTORS, RESIDENTS ALARMED
With only the timing of an attack apparently in doubt, oil prices soared to a six-month high, lifting U.S. energy shares and the overall U.S. market.
But some emerging markets closed lower again on Wednesday because of investor jitters over where the international escalation of Syria's civil war might lead - however much Obama and his allies may hope to limit it to a short punitive mission.
Neighbouring Turkey, a NATO member, put its forces on alert. Israel mobilised some army reservists and bolstered its defences against missile strikes from either Syria or Lebanon.
Syria's envoy to the United Nations said he had asked Ban to have the team investigate three new attacks by rebel groups.
People in Damascus, wearied by a civil war that has left the capital ringed by rebel-held suburbs, braced for air strikes.
In a city where dozens of military sites are mixed in among civilian neighbourhoods, some were leaving home in the hope of finding somewhere safer, although many doubted it was worth it.
"Every street, every neighbourhood has some government target," said a nurse in the city centre. "Where do we hide?"
At grocery stores, shoppers loaded up on bread, dry goods and cans. Bottled water and batteries were also in demand.
Numerous factors, including weather and assessments of Syrian air defences, may affect the timing of strikes. Analysts expect cruise missiles to be launched from U.S. ships in the Mediterranean. Aircraft could also play a role, as may forces from other NATO powers, notably Britain and France.
Obama is waiting for a U.S. intelligence report, although its findings are in little doubt. U.S. officials have already blamed Assad for the attacks on August 21. U.S. sources suggested that the intelligence cache included intercepted communications between Syrian officials but that those contained no "smoking gun" and were not likely to be declassified for public release.
British Prime Minister David Cameron has recalled parliament to debate the Syria crisis on Thursday. He should be able to secure cautious support, despite widespread misgivings among Western voters about new entanglements in the Muslim world. But British action is unlikely before lawmakers have had their say.
Although decisive action against Syria is strongly backed by many in the U.S. Congress, a growing number of lawmakers are pressing the president to consult them and receive congressional authorization before ordering use of force.
U.S. House of Representatives Speaker John Boehner urged Obama on Wednesday to make the case personally to Congress and the American people for potential military action in Syria.
The prospect of a Group of 20 summit in St. Petersburg next Thursday may also weigh in calculations over timing any strikes. Russian host President Vladimir Putin has made clear his view that Western leaders are using human rights as a pretext to impose their will on other sovereign states.
"The West behaves like a monkey with a grenade in the Islamic world," Russian Deputy Prime Minister Dmitry Rogozin tweeted on Wednesday. Western leaders in the G20 may prefer to have any strikes on Syria completed before the summit starts.
As diplomats from Russia, China, Britain, France and the United States met at the United Nations, Moscow said Britain was "premature" in seeking a Security Council resolution for "necessary measures" to protect Syrian civilians.
But U.S. State Department spokeswoman Marie Harf told reporters, "The Syrians cannot continue to hide behind Russian intransigence at the Security Council."
British Foreign Secretary William Hague said Russia and China might veto the move but added, "It's time the U.N. Security Council shouldered its responsibilities on Syria which for the last two and a half years it has failed to do."
A senior Western diplomat said, "Of course there will be a Russian veto, but that's part of the objective - to show that we tried everything and the Russians left us no choice.
"The Americans want to go quickly."
China's official newspaper also criticised on Wednesday what it saw as a push for illegal, Iraq-style "regime change" - despite U.S. denials that Obama aims to overthrow Assad.
The U.S.-led NATO alliance said evidence pointed to Assad's forces having used gas, calling it a threat to global security.
Ban's special envoy for Syria, Algerian diplomat Lakhdar Brahimi, said that "international law is clear" in requiring council authorisation for any military action. But Western leaders say precedents, including NATO's bombing of Russian ally Serbia in 1999 during the Kosovo war, allow them to protect civilians.
There was tension between the United Nations and Western governments. One U.N. official said: "The U.N. is annoyed and feels the Western powers haven't shared data or evidence with them, which is a problem. It kind of undercuts U.N. authority."
German Chancellor Angela Merkel and the British prime minister agreed in a telephone discussion with Cameron that Syria's government should not to go unpunished for the poison gas attack on its own people, Berlin said on Wednesday.
Syria's civil war has killed more than 100,000 people since 2011 and driven millions from their homes, many crossing borders into Turkey, Lebanon, Jordan and Iraq.
It has heightened tensions between Assad's sponsor Iran and Israel, which bombed Syria this year, and has fuelled sectarian bloodshed in Lebanon and in Iraq, where bombs killed more than 70 people on Wednesday alone.
Iranian Supreme Leader Ayatollah Ali Khamenei said on Wednesday that U.S. action would be "a disaster for the region."
(Additional reporting by Wiliam Maclean and Mariam Karouny in Beirut, Guy Faulconbridge and Andrew Osborn in London, Steve Gutterman in Moscow, Tom Miles and Stephanie Nebehay in Geneva, Yeganeh Torbati and Yara Bayoumy in Dubai, Anthony Deutsch and Thomas Escritt in The Hague, Ben Blanchard in Beijing, Arshad Mohammed, Mark Hosenball, Matt Spetalnick and Patricia Zengerle and Phil Stewart in Washington; Writing by Alastair Macdonald; Editing by Will Waterman, David Stamp and Peter Cooney)