US Secretary of State John Kerry made an impassioned plea to the Syrian regime to seize the moment Tuesday to try and make peace and help destroy its chemical weapons.
The top US diplomat, who has been leading the Obama administration's charge for military strikes, said he expected Russia would later in the day send proposals on how Syria could secure its deadly stock of mustard and sarin gas.
In another day of fast-moving diplomatic drama, Syrian Foreign Minister Walid al-Muallem said Damascus wanted to join the international treaty banning chemical weapons.
Directly addressing Muallem and President Bashar al-Assad, Kerry said he hoped the two men "would take advantage of this opportunity as a moment to try to make peace in Syria."
"Help us in the next days working with Russia to work out the formula by which those weapons can be transferred to international control and destroyed," Kerry pleaded during an online discussion hosted by Google.
After talking with Russian Foreign Minister Sergei Lavrov, Kerry said he expected details of the plan to be sent to Washington "during the course of the day," but he insisted it must include "consequences" if it turns out to be a delaying tactic to avoid threatened US military action.
Assad's regime is accused of using chemical weapons in an August attack near Damascus, which Washington says killed 1,400 people.
Lavrov "had some interesting observations about the ways in which he thinks we might be able to achieve this," Kerry said.
"If we can in fact secure all of the chemical weapons in Syria, through this method, clearly that's by far the most preferable, and would be a very significant achievement," he said.
Kerry stressed the proposals must be an "ongoing verifiable process" with full international access to all of the sites in question. "This cannot be a game. And that we have made very, very clear to the Russians," he said.
The United States, France and Britain are working on a resolution to go before the United Nations.
"We need a full resolution from the Security Council in order to have the confidence that this has the force that it ought to have," Kerry said.
"Common sense tells us that we don't want to buy into something that isn't going to get the job done. So this has to be transparent, accountable, fully implementable and a clearly verifiable process and we're going to have to work at how that's going to be achieved," the top US diplomat said.
"But it's also going to have consequences if games are played or somebody tries to undermine this."
At an earlier Congress hearing, Defense Secretary Chuck Hagel said while everyone was hopeful the move could be "a real solution to the crisis" the threat of "credible, real" US military action had to remain on the table.
Kerry told lawmakers Syria had about "1,000 metric tonnes of numerous chemical agents including sulfur, mustard gas and binary components for sarin gas and VX."
US experts were already working on how to implement the "exceedingly difficult" task of securing and destroying the weapons, he told the House Armed Services Committee.
President Barack Obama is to address the nation later Tuesday as he seeks to build support for limited US military strikes, and Kerry warned that Washington would not "wait too long" for the Russian proposal.
Hagel added: "We must be very clear-eyed and ensure that it is not a stalling tactic by Syria and its Russian patrons.
"The threat of a US military action, the credible, real threat of US military action, must continue as we are talking today."
Top military officer General Martin Dempsey said Obama "has not yet given me the final decision" on what would be the target of any strikes.
But asked whether innocent people could be killed, the chairman of the Joint Chiefs of Staff said "you can make that assumption because war is an imperfect science."
He assured however that every effort would be made to protect civilians.
"Part of the targeting criteria I've been given by the president is to achieve a collateral damage estimate of low," he said.