Western powers could attack Syria within days, envoys from the United States and its allies told rebels fighting President Bashar Assad, sources who attended the meeting between the groups told Reuters on Tuesday.
U.S. forces in the region are "ready to go," Defense Secretary Chuck Hagel said, as Washington and its European and Middle Eastern partners honed plans to punish Assad for a major poison gas attack last week that killed hundreds of civilians.
Several sources who attended the meeting in Istanbul Tuesday between Syrian opposition leaders and diplomats from Washington and other governments told Reuters that the rebels were told to expect military action and to get ready to negotiate a peace.
"The opposition was told in clear terms that action to deter further use of chemical weapons by the Assad regime could come as early as in the next few days, and that they should still prepare for peace talks at Geneva," one of the sources said.
Ahmad Jarba, president of the Syrian National Coalition, met envoys from 11 states in the Friends of Syria group, including Robert Ford, the U.S. ambassador to Syria, at an Istanbul hotel.
United Nations chemical weapons investigators, who finally crossed the frontline to take samples on Monday, put off a second trip to rebel-held suburbs of Damascus. But Washington said it already held Assad responsible for a "moral obscenity" and President Barack Obama would hold him accountable.
Facing Russian and Chinese disapproval that will complicate hopes for a united front backed by international law, and keen to win over wary voters at home, Western leaders seem in no rush to pull the trigger. British Prime Minister David Cameron called Parliament back from recess for a session about Syria on Thursday.
U.N. experts trying to establish what killed hundreds of civilians in rebel-held suburbs of Damascus last Wednesday were finally able to cross the frontline on Monday to see survivors — despite being shot at in government-held territory. But they put off a second visit until Wednesday.
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However, U.S. officials said President Barack Obama already had little doubt Assad's forces were to blame. Turkey, Syria's neighbor and part of the U.S.-led NATO military pact, called it a "crime against humanity" that demanded international reaction.
The Syrian government, which denies using gas, said it would press on with its offensive against rebels around the capital. Foreign Minister Walid Moualem said U.S. strikes would help al-Qaeda allies but called Western leaders "delusional" if they hoped to aid the rebels to create a balance of power in Syria.
In Britain, whose forces have supported the U.S. military in a succession of wars, Cameron called for an appropriate level of retribution for using chemical weapons.
"Our forces are making contingency plans," a spokesman for Cameron told reporters. London and its allies would make a "proportionate response" to the "utterly abhorrent" attack.
Top generals from the United States and European and Middle Eastern allies met in Jordan Monday for what could be a council of war.
On Monday, U.S. Secretary of State John Kerry said: "President Obama believes there must be accountability for those who would use the world's most heinous weapons against the world's most vulnerable people ... What we saw in Syria last week should shock the conscience of the world.
"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."
How such an intervention, likely to be limited to some form of air strike, would affect the course of Syria's civil war is far from clear. Obama, Cameron, and French President Francois Hollande face tough questions on how far they want to use force to achieve a long-stated common goal of forcing Assad from power.
Turmoil in Egypt, whose 2011 uprising inspired Syrians to rebel, has underlined the unpredictability of revolutions. And the presence of Islamist militants, including allies of al-Qaeda in the Syrian rebel ranks, has given Western leaders pause. They have held back so far from helping Assad's opponents to victory.
Russia, a major arms supplier to Assad, has said rebels may have released the gas and warned against attacking Syria. Russian Deputy Foreign Minister Gennady Gatilov criticized Washington for canceling bilateral talks on Syria that were set for Wednesday.
"Working out the political parameters for a resolution in Syria would be exceptionally useful now, when the threat of force hangs over this country," Gatilov wrote on Twitter.
The Syrian conflict has split the Middle East along sectarian lines. Shiite Muslim Iran has supported Assad and his Alawite minority against mainly Sunni rebels, some of them Islamists, who have backing from Gulf Arab states.
In Tehran, a foreign ministry spokesman said: "We want to strongly warn against any military attack in Syria. There will definitely be perilous consequences for the region.
"These complications and consequences will not be restricted to Syria. It will engulf the whole region."
Syrian foreign minister Moualem, who insisted the government was trying to help the U.N. inspection team, told a news conference in Damascus that Syria would hit back if attacked.
"We have means of defending ourselves, and we will surprise them with these if necessary," he said. "If we face aggression, we will defend ourselves. We will not hesitate to use any means available. But I will not specify what those would be."
Assad's forces made little or no response to three attacks by Israeli aircraft earlier this year which Israeli officials said disrupted arms flowing from Iran to Lebanon's Hezbollah.
China, which has joined Moscow in vetoing measures against Assad in the U.N. Security Council, is also skeptical of Western readiness to use force to interfere with what it sees as the internal affairs of other countries. Beijing's official news agency ran a commentary on Tuesday recalling the United States invaded Iraq in 2003 on the grounds that it possessed banned weapons — which were never found.
"The recent flurry of consultations between Washington and its allies indicates that they have put the arrow on the bowstring and would shoot even without a U.N. mandate," the Xinhua agency said. "That would be irresponsible and dangerous."
The continued presence of United Nations experts in Damascus may be a factor holding back international military action.
A U.N. statement said the investigators had put off a second visit to the affected areas until Wednesday to prepare better.
Some residents of the capital are getting anxious.
"I've always been a supporter of foreign intervention but now that it seems like a reality, I've been worrying that my family could be hurt or killed because they live near a military installation," said one woman, Zaina, who opposes Assad.
"I'm afraid of a military strike now."
But another woman who supports the president but did not want her name published said she refused to let herself worry:
"Bombing, kidnapping, killing — we face it every day already," she told Reuters.
"If it brings an end to this faster, frankly I'd welcome it. But honestly I don't really believe the Americans will do it."
The Washington Post cited senior U.S. officials as saying Obama is weighing a military strike that would be of limited scope and duration, while keeping the United States out of deeper involvement in the civil war.
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Such an attack would probably last no more than two days and see cruise missiles launched from ships — or, possibly, long-range aircraft — striking military targets not directly related to Syria's chemical weapons arsenal, the newspaper said.
Such a move was, it said, dependent on three factors: completion of an intelligence report assessing the Syrian government's culpability in the chemical attack, consultation with allies and the U.S. Congress, and determination of a justification under international law. U.S. warships armed with cruise missiles are already positioned in the Mediterranean.
Opposition activists have said at least 500 people and possibly twice that many were killed last week when rockets laden with poison, possibly the nerve gas sarin or something similar, landed in areas around Damascus where rebels are holding out in the face of heavy bombardments by government forces.
If confirmed, it would be the worst chemical weapons attack since Saddam Hussein gassed thousands of Iraqi Kurds in 1988.
In Israel, citizens have been lining up for gas masks in case Assad responds to a Western attack by firing on Israel, as Iraq's Saddam did in 1991.
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