WASHINGTON — US naval forces are moving closer to Syria as President Barack Obama considers military options for responding to the alleged use of chemical weapons by the Assad government. The president emphasized that a quick intervention in the Syrian civil war was problematic, given the international considerations that should precede a military strike. The White House said the president met Saturday with his national security team to consider possible next steps by the United States. Officials say once the facts are clear, Obama will make a decision about how to proceed. Defense Secretary Chuck Hagel declined to discuss any specific force movements while saying that Obama had asked the Pentagon to prepare military options for Syria. US defense officials told The Associated Press that the Navy had sent a fourth warship armed with ballistic missiles into the eastern Mediterranean Sea but without immediate orders for any missile launch into Syria. US Navy ships are capable of a variety of military action, including launching Tomahawk cruise missiles, as they did against Libya in 2011 as part of an international action that led to the overthrow of the Libyan government. “The Defense Department has a responsibility to provide the president with options for contingencies, and that requires positioning our forces, positioning our assets, to be able to carry out different options — whatever options the president might choose,” Hagel told reporters traveling with him to Asia. Hagel said the US is coordinating with the international community to determine “what exactly did happen” near Damascus earlier this week. According to reports, a chemical attack in a suburb of the capital killed at least 100 people. It would be the most heinous use of chemical weapons since Iraqi leader Saddam Hussein gassed thousands of Kurds in the town of Halabja in 1988. Meanwhile Doctors without Borders (MSF) said on Saturday that around 3,600 patients displaying “neurotoxic symptoms” flooded into three Syrian hospitals on the day of alleged chemical weapons attacks, and 355 of them died. The victims all arrived within less than three hours of each other, and MSF director of operations Bart Janssens said the pattern of events and the reported symptoms “strongly indicate mass exposure to a neurotoxic agent.” “Medical staff working in these facilities provided detailed information to MSF doctors regarding large numbers of patients arriving with symptoms including convulsions, excess saliva, pinpoint pupils, blurred vision and respiratory distress,” he said. — Agencies