Positions hardened in the international standoff over Syria, as U.S. officials said privately that a flood of previously undisclosed intelligence, including satellite images and intercepted communications, convinced them the Syrian regime had used chemical weapons against its own people.
French, U.K. and U.S. military officials talked Tuesday about coordinating their response to the alleged attacks.
The current U.S. position, reflected in a set of tough remarks Tuesday by Vice President Joe Biden, represents a dramatic turnaround from last week. As late as Friday, Secretary of State John Kerry was pressuring Syria to let United Nations inspectors visit the affected areas to help determine the veracity of reports of a chemical attack.
Less than 48 hours later came a marked shift in tone. In an email on Sunday, White House National Security Adviser Susan Rice told U.N. Ambassador Samantha Power and other top officials that the U.N. mission was pointless because the chemical weapons evidence already was conclusive, officials said. The U.S. privately urged the U.N. to pull the inspectors out, setting the stage for President Barack Obama to possibly move forward with a military response, officials said.
The weekend turnabout was spurred by new intelligence that convinced Mr. Obama's top national security advisers that forces loyal to Mr. Assad had used chemical weapons and that they were actively trying to cover up evidence of it even while they shelled the site of the attack, officials said. The White House also became convinced the regime was stalling the U.N. inspection to delay a U.S. response, they said.
One crucial piece of the emerging case came from Israeli spy services, which provided the Central Intelligence Agency with intelligence from inside an elite special Syrian unit that oversees Mr. Assad's chemical weapons, Arab diplomats said. The intelligence, which the CIA was able to verify, showed that certain types of chemical weapons were moved in advance to the same Damascus suburbs where the attack allegedly took place a week ago, Arab diplomats said.
The U.S. position changed rapidly. In a CNN interview recorded Thursday, Mr. Obama highlighted the dangers of intervening with force in Syria without U.N. Security Council approval. By Saturday night, the administration had set a different course—if the U.S. chose to strike, it would do so with allies and without the U.N., in order to sidestep an expected Russian veto.
For a White House that has tried to differentiate itself from its predecessor's war in Iraq, the bar for using intelligence to justify a military operation is high, current and former officials say. The administration plans to make public this week at least some of its evidence before taking any military action, which it says would be aimed at punishing, not removing, Mr. Assad.
Ever since the start of the civil war in 2011, Mr. Obama made clear to his advisers that their top priority would be to prevent the use and spread of Mr. Assad's chemical weapons. To that end, the Pentagon and the CIA put an early focus on tracking special Syrian forces which control the country's chemical stocks, using spy satellites and allied spy networks on the ground.
That tracking effort, aided by Israeli and Jordanian agents, expanded in recent months, particularly since the U.S. concluded in June Mr. Assad's forces had used chemical weapons on a small scale.
A key battleground for Mr. Assad involved a cluster of Damascus suburbs including the Eastern Ghouta region, the last remaining district around Damascus not under partial or total regime control. On Wednesday morning, Mr. Assad's forces launched "Operation City Shield" against rebel positions in the area.
Syrian officials described the operation as a "pre-emptive strike," citing intelligence showing that rebel fighters trained outside Syria were amassing in that district and planned a massive attack on Damascus.
The CIA and Saudi intelligence have been training rebels at a base in Jordan, but officials wouldn't comment on their movements and activities.
Wednesday's bombardment included chemical weapons on a scale unseen in the 2 ½-year conflict, American officials said. Syria denied it used chemical weapons and has blamed rebels.
Video accounts quickly popped up on YouTube. Western intelligence agencies had their own video images, sent to them by their own informants, verifying the scope of the incident.
Within hours, the administration launched parallel campaigns: one diplomatic to force Syria to let U.N. inspectors visit the site; the other fact-finding, to gather evidence of what happened.
On Thursday, Mr. Kerry took the unusual step of calling Syrian Foreign Minister Walid Moallem to demand immediate access to the areas, officials said. Mr. Moallem said he told Mr. Kerry: "We have a natural interest in exploring the truth. I will work to implement Syria's national interest." He also told Mr. Kerry that those districts weren't under government control.
American officials said Mr. Kerry told Mr. Moallem that rebel forces could ensure the safety of the U.N. investigators.
The call "ended in a cordial way" after 10 minutes, Mr. Moallem said.
That same day, U.N. Secretary General Ban Ki-moon also called on the Syrians to provide immediate access.
A formal U.N. request, however, wasn't made until Saturday, according to U.N. and Syrian officials.
All day Friday, the U.N. inspections team remained in Damascus.
Mr. Obama's position already had shifted by Saturday morning, when he convened a National Security Council meeting in the White House Situation Room, officials said. "The going-in proposition, even leading into the meeting, was everything was pointing to the same conclusion," a senior administration official said.
During the White House meeting, officials reviewed the latest intelligence and the delays facing the U.N. team. Another senior administration official said the Syrians were "playing games" with the U.N. team.
On Sunday morning in Damascus, Angela Kane, the U.N. disarmament chief, was granted an audience with Mr. Moallem. The U.N. team had hoped to start field work immediately, but remained grounded until Monday.
Sunday morning in Washington, Mr. Obama's aides reviewed satellite images that officials said showed how continued shelling was obliterating evidence of chemical-weapon use, officials said.
Early that morning, Ms. Rice sent the email to Ms. Power and others, officials said. "The investigation is…too late, and will actually tell us what we already know: CW was used," Ms. Rice wrote, using the abbreviation for chemical weapons. "It won't even tell us by whom, which we already know."
About 10 a.m. Sunday, senior administration officials issued a sharply worded statement that made clear that the U.S. intended to respond to "this indiscriminate use of chemical weapons"—the only question was when and how.Instead of seizing on Syria's decision to let the inspectors visit the site to tone down its rhetoric and avoid an escalation, the White House appeared to be digging in. On Monday night and Tuesday, Mr. Kerry telephoned key lawmakers with a message: The administration was now convinced that the regime was behind last Wednesday's chemical weapons. "We have no doubt that they did it," Mr. Kerry told them, according to an official briefed on the calls.
On Monday morning, the U.N. team finally headed out from the Four Seasons Hotel in Damascus to visit clinics and makeshift field hospitals in the Ghouta districts. They collected samples and conducted interviews with patients and medical staff.
From the start, the White House put little stock into possible action through the U.N. Security Council, officials said, citing Russia's support for Mr. Assad. "There was not a plan or an expectation that the U.N. would be a likely course of action for building a coalition for some type of intervention in Syria," a senior administration official said.
—Carol E. Lee, Margaret Coker, Joe Lauria and Jay Solomon contributed to this article. Write to Adam Entous at adam.entous@wsj.com, Sam Dagher at sam.dagher@wsj.com and Siobhan Gorman at siobhan.gorman@wsj.com
