The United States could hit Syria with three days of missile strikes, perhaps beginning Thursday, in an attack meant more to send a message to the Syrian regime than to cripple its military, senior U.S. officials told NBC News.
The options are not about regime change, the White House said.
The disclosure added to a growing drumbeat around the world for military action against Syria, believed to have used chemical weapons in recent days against scores of civilians and rebels who have been fighting the government for two years.
In three days of strikes, the Pentagon could assess the effectiveness of the first wave and target what was missed in further rounds, the senior officials said.
British Prime Minister David Cameron cautioned that no decision on military strikes had been made. The White House said President Barack Obama has a variety of options, not just an attack, Reuters reported.
But some analysts said Washington had few options other than force in order to preserve its credibility in light of statements by Obama drawing a line against Syrian use of chemical weapons in its civil war and more recently by Secretary of State John Kerry on Monday.
"Once you make those kinds of comments ... you risk losing your credibility if you don't then follow through on them," Jacob Shapiro, Middle East analyst for Stratfor, told CNBC's "Street Signs."
"I'm not going to tell you that it's an absolute sure thing, but I think there's a very high probability that there will be some kind of punitive, limited strike in Syria in the next few days."
News of a possible attack sent U.S. stock prices skidding—the Dow fell to a two-month low—while oil prices surged to a six-month high and Treasury prices rose. European stocks also suffered their biggest drop in two months.
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The U.S. officials' comments about the possible timing for military action came a day after another round of telephone diplomacy by Obama, who held discussions with Australian Prime Minister Kevin Rudd and French President Francois Hollande.
Hollande said Tuesday that France stood ready "to punish" the perpetrators of the attack and would increase its military support to the Syrian opposition.
Cameron recalled Parliament from vacation on Tuesday and said lawmakers would vote Thursday on a proposal for action.
Also Tuesday, Saudi Foreign Minister Saud al-Faisal said a "decisive and serious" international stand was required against Damascus. The Arab League blamed the Syrian government for the deadly attack and said that those responsible should face international justice. It called on U.N. Security Council members to overcome their differences and take action to end the killing there.
Support from the Arab League, even if limited, would provide crucial diplomatic cover for a Western strike on Syria. Action through the United Nations is unlikely because Russia, which supports Syrian President Bashar Assad, has a veto in the Security Council.
Defense Secretary Chuck Hagel, meanwhile, told the BBC the U.S. military is "ready to go" if Obama orders action.
We have moved assets in place to be able to fulfill and comply with whatever option the president wishes to take," Hagel said during a trip to Brunei, according to a partial transcript provided by the BBC. Asked if the U.S. military was ready to respond just "like that," Hagel said: "We are ready to go, like that."
Hagel's comments came a day after Kerry laid the groundwork for possible military action, saying there needed to be "accountability" for the use of chemical weapons.
Hagel said the United States would have intelligence to present "very shortly" about the attack. But he noted after calls with his British and French counterparts that there was little doubt among most U.S. allies that "the most base ... international humanitarian standard was violated."
Assad called the claims that Syria used chemical weapons "preposterous."
The Russian foreign minister, Sergei Lavrov, said it would be a "very grave violation of international law," and China said through its government-run news service that the U.S. must refrain from "hasty armed intervention."
Facing Russian and Chinese disapproval that could dampen prospects for proposed peace talks in Geneva, Assad's foes have vowed to punish a poison gas attack in some rebel-held districts of Damascus on Aug. 21 that killed hundreds.
U.N. experts trying to establish what exactly happened in the attack were finally able to cross the front line on Monday to see survivors—despite being shot at in government-held territory. But they put off a second visit until Wednesday.
In markets on Tuesday, Brent crude climbed to a six-month high above $114, and U.S. crude settled at $109.01. It was the first time it settled above $109 since Feb. 24, 2012. Though Syria is not a major oil producer, Western intervention there could lead to a wider conflict in the volatile Middle East, which pumps a third of the world's oil.
"This is a huge deal, particularly for the oil markets," Helima Croft, commodities research head at Barclays, said on CNBC's "Squawk on the Street."
—Dubai's stock market tumbled 7.0 percent on Tuesday, its heaviest one-day loss since the emirate's corporate debt crisis in November 2009.
—Israel's shekel fell to a six-week low against the dollar and share prices dropped 2 percent.
—The Indian rupee and Turkish lira tumbled to record lows.
—By CNBC.com with NBC News and Reuters.