With a flurry of diplomatic signals and activity, U.S. officials sought Tuesday to lay the groundwork for a possible military strike on Syria in response to last week's suspected chemical weapons attack that Washington blames on President Bashar al-Assad's regime.
The White House offered legal justification, with spokesman Jay Carney telling reporters that the large-scale use of chemical weapons in Syria presented a national security threat to the United States that required a response.
Carney reiterated that President Barack 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 continued to review options, Carney said, adding that "nothing has been decided" but assuring 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.
Secretary of Defense Chuck Hagel and Secretary of State John Kerry consulted allies and indicated potential imminent action by a coalition likely to include key NATO partners and regional powers.
Days after the United States 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
Obama spoke Tuesday with Canadian Prime Minister Stephen Harper about "potential responses" in Syria, according to a White House statement.
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.
Debate within the administration over what information to release included the CIA and other intelligence agencies arguing 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 Carney and Kerry, made releasing underling 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.
Legislators: Syria response affects Iran
To Republican Rep. Peter King of New York, an influential member of the House Homeland Security Committee, the U.S. response to the Syria situation will influence another regional proliferation issue -- Iran's potential development of nuclear weapons.
Obama "time and again has basically said that Iran will not be allowed to have nuclear weapons, that's the red line," King told CNN on Monday, adding that failure to enforce a similar threat against Syria on chemical weapons would undermine the president.
"This is as much a warning to Iran as I see it, as it is action against Syria," King said.
Democratic Sen. Jack Reed of Rhode Island, a member of the Senate Armed Services Committee, told CNN on Monday that the United States should only act in concert with an international coalition from at least NATO allies and Arab League members.
"Without their participation, it looks as if this is just a Western-vs.-Islamic struggle. It's not," Reed said. "This is to vindicate a basic rule of international law that these weapons will not be used, not by Iran, not by any power."
Reed said the most realistic option would be cruise missiles launched from U.S. Navy ships at sea, noting