With a flurry of comments and activity, U.S. officials sought Tuesday to lay the groundwork for a military strike in Syria -- though some in Washington are pushing back.
The moves by top members of President Barack Obama's administration come less than a week after rebels claim more than 1,300 people were killed in a Syrian government, most of them dying from use of chemical weapons.
The White House offered legal justification for a strike, with spokesman Jay Carney telling reporters the large-scale use of chemical weapons in Syria presented a national security threat to the United States that required a response.
Carney said Obama had yet to make a final decision on how to respond to what U.S. officials characterize as the worst chemical weapons attack since former Iraqi strongman Saddam Hussein launched a poison gas attack that killed thousands of Kurds in 1988.
The president continues to review options, Carney said, adding "nothing has been decided." Carney assured reporters some sort of response will come.
"Allowing the use of chemical weapons on a significant scale to take place without a response would present a significant challenge to or threat to the United States' national security," he said.
Vice President Joe Biden made clear the administration's view of who was to blame, telling the American Legion that "there is no doubt who is responsible for the heinous use of chemical weapons -- the Syrian regime."
On the same day Obama talked with Canadian Prime Minister Stephen Harper and UK Prime MInister David Cameron, Secretary of Defense Chuck Hagel and Secretary of State John Kerry consulted allies and indicated potentially imminent action by a coalition likely to include key NATO partners and regional powers.
The United States has already moved warships armed with cruise missiles into the region. Hagel told the BBC on Tuesday that forces were ready to carry out a strike if ordered. A senior Defense Department official told CNN that any strike could be completed "within several days."
"We are ready to go, like that," Hagel told the BBC, adding that "the options are there, the United States Department of Defense is ready to carry out those options."
White House: No decision yet
Options available to Obama range from ordering limited missile strikes to continued diplomatic efforts labeled by critics as a "do-nothing" approach.
The White House has ruled out sending ground troops to Syria or implementing a no-fly zone to blunt al-Assad's aerial superiority over rebels fighting to oust his regime.
On Monday, Carney said that the first step toward a military response in Syria would be the public release of a U.S. intelligence report on the August 21 event near Damascus that reportedly killed and wounded thousands.
A U.S. official who was not authorized to speak on the record told CNN that release of the intelligence report was planned for Tuesday, but Carney later said it would come out some time this week.
Another official told CNN the intelligence report would include forensic evidence and intercepted communications among Syrian military commanders.
Yet there's been some debate, within the administration, over what information should be released. The CIA and other intelligence agencies, for instance, have argued there was no need, and perhaps harm, in divulging details, two U.S. officials told CNN's Evan Perez.
One of the officials noted that the U.S. conclusion that the Syrian government was responsible, as expressed by Biden and Kerry, made releasing underlying intelligence superfluous.
Carney said Tuesday there was "no doubt" in the administration that chemical weapons were used by the al-Assad government, telling reporters that "we see no evidence of any alternative scenario."
For almost two years, Obama has avoided direct military involvement in Syria's civil war, only escalating aid to rebel fighters in June after suspected smaller-scale chemical weapons attacks by Syrian government forces.
However, last week's attack obliterated the "red line" Obama set just over a year ago against the use of Syria's chemical weapons stocks.
Legislator: Congress can't 'be pushed aside'
Yet some in Congress say that before Obama orders any strike, they should go through them first.
A group of 31 Republican and six Democratic lawmakers on Tuesday sent a letter to the president urging him "to consult and receive authorization" before authorizing any such military action.
"Any U.S. military action could bring serious consequences or further escalation," said Rep. Ed Royce, a California Republican who chairs the House Foreign Affairs Committee and was not among the letter's initial signatories. "The president should be making the case to the American public, and his administration should come to Congress to explain their plans.