The United States is waiting to see a Russian proposal to put Syria's chemical weapons stock under international control, but will not wait for long, top diplomat John Kerry said Tuesday.
While everyone was hopeful the move could be "a real solution to the crisis," said Defense Secretary Chuck Hagel, he warned the threat of "credible, real" US military action had to remain on the table.
Kerry alleged Syria had about "1,000 metric tonnes of numerous chemical weapons" including components for mustard and sarin gas, some of which was unmixed, and some of which was stored in tanks.
"Yesterday, we challenged the regime to turn them over to the secure control of the international community so that they could be destroyed," he told lawmakers.
Such a move "would be the ultimate way to degrade and deter" the arsenal held by Syrian President Bashar al-Assad, he told the House Armed Services Committee.
US experts were already working on how to carry out such an "exceedingly difficult" task, he said, as Russian Foreign Minister Sergei Lavrov mulls a proposal on reining in Syria's chemical weapons.
"We're waiting for that proposal. But we're not waiting for long," Kerry said.
President Barack Obama -- who is due to address the nation later Tuesday -- "will take a hard look at it, but it has to be swift. It has to be real. It has to be verifiable," Kerry insisted.
He added, however, that "nothing had changed" with respect to Obama's call for Congress to vote to approve a limited military strike on the Syrian regime, accused of using sarin gas in an attack near Damascus last month.
"We must be very clear-eyed and ensure that it is not a stalling tactic by Syria and its Russian patrons," Hagel said of the Russian proposal.
"The threat of a US military action, the credible, real threat of US military action, must continue as we are talking today," he insisted.
The United States had "a full range of options" in any military action aimed at degrading Syria's chemical weapons stock which could target "the command and control of those who chose to use them, the means of delivery, and some of the other resources that the regime uses to protect itself," said top military officer General Martin Dempsey.
"Importantly, the president has not yet given me the final decision on those target packages," he told lawmakers.
Asked whether innocent people could be killed in any US strike, the chairman of the Joint Chiefs of Staff said "you can make that assumption because war is an imperfect science."
But he assured that every effort would be made to protect civilians.
"You can also be sure that part of the targeting criteria I've been given by the president is to achieve a collateral damage estimate of low."