Striking a tough tone, US Secretary of State John Kerry opened swiftly convened talks with Russia on Syria's chemical weapons by bluntly rejecting a Syrian pledge to begin a "standard process" by turning over information rather than weapons - and nothing immediately.
That will not do, Mr Kerry declared at an opening news conference in Geneva, Switzerland, with stony-faced Russian Foreign Minister Sergey Lavrov at his side. "The words of the Syrian regime in our judgment are simply not enough."
"This is not a game," Mr Kerry said of the latest developments in a series that has rapidly gone from deadly chemical attacks to threats of retaliatory US air strikes to Syrian agreement with a Russian plan to turn over the weapons and, finally, to the crucial matter of working out the difficult details.
"We believe there is nothing standard about this process at this moment because of the way the regime has behaved," Mr Kerry declared. And he kept alive the threat of US military action, saying the turnover of weapons must be complete, verifiable and timely - "and finally, there ought to consequences if it doesn't take place".
That was an apparent reference to a comment President Barack Obama made in his Syria speech on Tuesday night, explaining why he felt the US needed to take action. Congress has shown little inclination to authorise military action, and a vote on that has been put off.
Mr Putin also warned that a US strike against Syria because of chemical weapons use could unleash new terrorist attacks. And he continued to maintain that there is "every reason to believe" the weapons were used by rebels and not by Syrian President Bashar Assad's military.
Mr Obama, for his part, said simply that he was hoping for "a concrete result" from the talks.
The back-and-forth was a stark indication of the challenging work ahead as Mr Kerry, Mr Lavrov and their teams of chemical weapons experts plunge into talks aimed at finding agreement on how to dismantle the chemical weapons amid the confusion and danger of Syria's civil war.
The distrust in US-Russia relations was on display even in an off-hand parting exchange at the news conference. Just before it ended, Mr Kerry asked the Russian translator to repeat part of Mr Lavrov's concluding remarks. When it was clear that Mr Kerry was not going to get an immediate re-translation, Mr Lavrov apparently tried to assure him that he had not said anything controversial. "It was OK, John, don't worry," he said. "You want me to take your word for it?" Mr Kerry asked Mr Lavrov. "It's a little early for that." They were smiling at that point.