U.S. repositions naval forces, no decision on Syria strike By Matt Spetalnick and Andrea Shalal-Esa WASHINGTON (Reuters) - 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. 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 al-Assad braved the front lines around Damascus to smuggle out tissue samples from victims of Wednesday's mass poisoning,. 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. "What we've seen indicates that this is clearly a big event, of grave concern," Obama said in an interview on CNN's "New Day" program that aired on Friday. Obama's caution contrasted with calls for action from NATO allies, including France, Britain and Turkey, where leaders saw little doubt Assad's forces had staged pre-dawn missile strikes that rebels say killed between 500 and well over 1,000 people. But two years into a civil war that has divided the Middle East along sectarian lines, a split between Western governments and Russia again illustrated the international deadlock that has thwarted outside efforts to halt the killing. Kerry, who took part in Thursday's meeting by secure video link, advocated the use of air strikes in White House meetings in early June preceding an announcement of military aid to the rebels, a person familiar with the talks said. Obama has shown no appetite for intervention. Additional reporting by Erika Solomon in Beirut, Mark Hosenball, Arshad Mohammed, Roberta Rampton, Jeff Mason, Andrea Shalal-Esa, Patricia Zengerle, Phil Stewart and Lesley Wroughton; Editing by Warren Strobel and Peter Cooney