While there is still no conclusive evidence, senior U.S. officials told NBC News on Friday that they believe the Syrian military did attack civilians with chemical weapons this week, prompting the Obama administration to consider how and when the U.S. military might respond.
President Barack Obama said he has shortened the time frame for the U.S. to decide whether it will act to halt the bloodshed, telling CNN that reports of a possible chemical weapons attack Wednesday near Damascus was "a big event of grave concern."
Three hospitals supported by Doctors Without Borders reported to the global humanitarian group that they received roughly 3,6000 patients showing neurotoxic symptoms in the less than three hours Wednesday — 355 of whom reportedly died, according to a statement released by the group on Saturday.
Although the group "can neither scientifically confirm the cause of these symptoms nor establish who is responsible for the attack," the reported symptoms "strongly indicate mass exposure to a neurotoxic agent," said Dr. Bart Janssens, Doctors Without Borders' director of operations, according to the statement.
U.S. officials said no decisions were made at a White House meeting among Obama's top advisers Thursday, which they described as the "most intense" discussion of possible military operations so far. Another meeting was scheduled for Saturday at the White House.
Josh Earnest, a White House spokesman, told reporters Friday that "all options remain on the table when it comes to Syria." But senior military officials who spoke on condition of anonymity told NBC News that any military response would likely be limited both in scope and impact.
"If the president wants to send a message" — most likely with limited airstrikes against a few targets — "we're good at sending messages," one official said. But if the White House wants to topple Syrian President Bashar Assad, "We're not able to do that" without a long-term military commitment, the official said.
Meanwhile, U.S. Defense Secretary Chuck Hagel suggested Friday that the United States was positioning naval forces and assets ahead of any move by Obama to order military action against Syria, Reuters reported.
"The Defense Department has responsibility to provide the president with options for all contingencies," Hagel told reporters while traveling in Malaysia, according to the wire service. "And that requires positioning our forces, positioning our assets to be able to carry out different options — whatever options the president might choose."
Whatever course the U.S. follows, it should be able to move quickly. U.S. officials said military planning and targeting have been underway for the last two years.
"We've already got the Syrian government and military targets lined up," one of the officials said — including the defense and interior ministries.
Officials stressed that any targets aren't yet part of an active attack plan. That would change only if Obama formally asks the Pentagon for options, they said.
Likely scenarios include a series of cruise missile attacks launched from two Navy guided-missile destroyers, the USS Gravely and the USS Barry, or from submarines positioned in the eastern Mediterranean Sea, the officials said. Two other guided-missile destroyers — the USS Mahan and the USS Ramage — are also in the region for a few more days if needed, although they have no specific orders involving Syria, a senior defense official said.
For now, the plans don't include boots on the ground or fighter or bomber aircraft, they said, which would significantly increase the logistics demands, expenses and risk.
Secretary of State John Kerry spent much of Thursday on the phone with UN Secretary General Ban Ki-moon and foreign ministers from the European Union, Russia, the Arab League and numerous Middle Eastern countries, stressing Washington's "concern and outrage" over reports from Syria, which the State Department said "shock the conscience."
Among the most disturbing developments is word that more than a million Syrian children have been forced to flee the country, most of them under the age of 11.
In an interview Friday with NBC News, António Gutierrez, the U.N. high commissioner for refugees, said millions more children were in immediate peril.
"The traumatic impact is so terrible," Gutierrez said. "These children will live with everything they have suffered for the rest of their lives."
Gutierrez called Syria "undoubtedly the greatest humanitarian disaster of the present century," adding: "We need to recognize that Syria faces the risk of a lost generation."