DAMASCUS, Syria (AP) - Fears of a possible U.S. strike against Syria's regime over an alleged chemical weapons attack rippled across the region Wednesday, as about 6,000 Syrians fled to neighboring Lebanon in a 24-hour period and Israelis scrambled for gas masks in case Damascus retaliates against them.
U.N. chief Ban Ki-moon pleaded for more time for diplomacy and to allow U.N. investigators to complete their work. The experts, wearing flak jackets and helmets, collected blood and urine samples from victims during a visit to at least one of the areas hit in last week's attack.
Seven days after chemical weapons were purportedly unleashed on rebel-held suburbs of the Syrian capital, momentum grew toward Western military action against President Bashar Assad's regime. At the same time, Syria's chief allies, Russia and Iran, warned of dire consequences for the region if any armed intervention is undertaken.
U.S. leaders, including Vice President Joe Biden, have charged that Assad's government was behind the Aug. 21 attack that Doctors Without Borders says killed at least 355 people. The White House says it's planning a possible military response while seeking support from international partners.
The U.S. has not presented concrete proof of Syrian regime involvement in the attack, and U.N. inspectors have not endorsed the allegations, although the U.N. envoy to Syria, Lakhdar Brahimi, said evidence suggests some kind of "substance" was used that killed hundreds.
Two senior Obama administration officials said U.S. intelligence agencies are drawing up a report laying out the evidence against Assad's government. The classified version would be sent to key members of Congress and a declassified version would be made public.
One of the officials said the administration is considering more than a single set of military strikes and "the options are not limited just to one day" of assault.
"If there is action taken, it must be clearly defined what the objective is and why" and based on "clear facts," the senior administration official said on condition of anonymity because he wasn't authorized to discuss internal deliberations publicly.
President Barack Obama is weighing a limited response that focuses on punishing the Syrian government for violating international agreements that bar the use of chemical weapons. Any U.S. military action, officials say, would not be aimed at toppling the Assad regime or vastly altering the course of Syria's civil war, which has already claimed 100,000 dead.
As the U.S., France and Britain push for military action, the U.N. secretary-general urged restraint to give U.N. inspectors time to finish their investigation, which began Monday.
"Let them conclude ... their work for four days and then we will have to analyze scientifically" their findings and send a report to the U.N. Security Council, Ban said. The U.N. said the analysis would be done "as quickly as possible."
At least 6,000 Syrians crossed into Lebanon in a 24-hour period through the main Masnaa crossing, including an estimated 4,000 on Wednesday, according to Lebanese security officials in the country's Bekaa Valley near the border. The normal daily influx is 500 to 1,000 refugees, depending on the level of fighting. The officials spoke on condition of anonymity in line with regulations.
Long lines of packed cars - some with suitcases strapped to roofs - were backed up at the frontier post, witnesses said. A security official said about 2,000 also crossed into Syria, but many of them said they were going in to evacuate relatives.
Effects were also evident in Israel, where large crowds lined up at gas-mask distribution centers. Maya Avishai of the Israeli postal service, which oversees gas mask distribution, said demand has tripled in recent days. About 5 million Israelis, roughly 60 percent of the population, now have gas masks, she said.