The United States on Friday was repositioning naval forces in the Mediterranean to give President Barack Obama the option for an armed strike on Syria, although officials cautioned that Obama had made no decision on military action.
A defense official, speaking on condition of anonymity, said the U.S. Navy would expand its presence in the Mediterranean to four destroyers from three.
Secretary of Defense Chuck Hagel, en route to Asia, said Obama had asked the Pentagon for options on Syria, where an apparent chemical weapons attack that killed as many as 1,000 civilians has upped pressure on Washington to respond.
"The Defense Department has responsibility to provide the president with options for all contingencies," Hagel said. "And that requires positioning our forces, positioning our assets, to be able to carry out different options - whatever options the president might choose." He did not elaborate.
The defense official, who was not authorized to speak publicly, said the USS Mahan, a destroyer armed with cruise missiles, had finished its deployment and was due to head back to its home base in Norfolk, Virginia. But the commander of the U.S. Sixth Fleet has decided to keep the ship in the region, the defense official said.
The official stressed the Navy had received no orders to prepare for any military operations regarding Syria.
Obama's senior national security advisers will convene at the White House this weekend to discuss U.S. options, including possible military action, against the Syrian government, another U.S. official said on Friday.
A senior State Department official said no final decisions were expected from the meeting, pending a further review of intelligence on the attack. Secretary of State John Kerry planned to attend via videoconference. The meeting was expected to take place on Saturday.
The U.S. president has been hesitant to intervene in Syria's 2 1/2-year-old civil war, sentiments he repeated earlier on Friday.
But, in a development that could increase the pressure on Obama, American and European security sources said that U.S. and allied intelligence agencies had made a preliminary assessment that chemical weapons were used by Syrian forces in the attack near Damascus this week.
The security sources, speaking on condition of anonymity, said the assessment was preliminary and, at this stage, they were still seeking conclusive proof, which could take days, weeks or even longer to gather.
Opponents of Syrian President Bashar Assad braved the front lines around Damascus to smuggle out tissue samples from victims of Wednesday's mass poisoning,.
The Syrian government denies being responsible and has in the past accused rebels of using chemical weapons, an allegation that Western officials have dismissed.
In his first public comments since Wednesday's attack in the Damascus suburbs, Obama called the incident a "big event of grave concern" and one that demanded U.S. attention, but said he was in no rush to get war-weary Americans "mired" in another Middle East conflict.
Members of Obama's National Security Council, the Pentagon, State Department and intelligence agencies met at the White House late on Thursday, but made no decisions on what to recommend, officials said.
One U.S. official acknowledged that the participants in Thursday's White House meeting aired "differing viewpoints," but rejected the notion that the administration, whose Syria policymaking has been marked by internal dissent in the past, was sharply divided on a response.
"It's not like people were screaming at each other," the official said.
International powers - including Russia, which has long shielded Assad from U.N. action - have urged Assad to cooperate with a U.N. inspection team that arrived on Sunday to pursue earlier allegations of chemical weapons attacks.
White House spokesman Josh Earnest said there was "some evidence" of chemical weapons use in the latest incident, but stopped short of saying an official conclusion was reached.
While the West accused Assad of a cover-up by preventing the U.N. team from visiting the scene, Moscow said the rebels were impeding an investigation.
The United Nations released data showing that a million children were among refugees forced to flee Syria, calling it a "shameful milestone."
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