Speaking in Laos, America's top diplomat said he had held a flurry of conversations with key parties including his French, Turkish, Russian and Saudi counterparts to try to get the talks to the starting line.
Representatives of the Syrian government and opposition had been set to meet in Geneva on Monday as part of a UN-endorsed 18-month peace plan.
But a dispute over whether armed groups should be able to sit at the table to represent the opposition appears poised to delay the talks.
Kerry said he had also spoken to the UN special envoy to Syria, Staffan de Mistura, "to make sure everybody is on the same page" ahead of negotiations.
"We are gonna have the meeting and they (the talks) are gonna start. We will have clarity I hope within 24 hours, somewhere like that, 48, something pretty soon," Kerry told reporters.
"The talks are going to take place soon, hopefully, hopefully, hopefully... I'm not in charge of that part. Staffan de Mistura has to make the decision," he added.
"We are talking about the modalities of the ceasefire, we are talking about the modalities of humanitarian or other confidence-building measures," Kerry said, adding he felt "positive" over the negotiations.
UN envoy de Mistura was due to hold a news conference later Monday in Geneva to discuss preparations.
Kerry's efforts are part of the biggest diplomatic push yet to end a civil war that has ground on for almost five years, claiming more than 250,000 lives.
