Kerry, in Laos after discussing the negotiations with officials in Switzerland and Saudi Arabia last week, said he expected there would be clarity soon about when the talks would start.
Today's scheduled start in Geneva has been pushed back due to disagreements over which groups can represent the opposition.
Kerry said that during his short stay in Laos, he had spoken to the UN special envoy for Syria and the foreign ministers of Russia, Saudi Arabia, France and Turkey.
"We're going to have the meeting and (the talks) are going to start," Kerry told reporters. "But what we are trying to do is to make absolutely certain that when they start everyone is clear about roles and what's happening so you don't go there and wind up with a question mark or a failure. You don't want to start Day One by not being able to make progress."
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He said his conversations with colleagues were mainly about how the cease-fire and confidence-building measures, such as opening up areas for humanitarian access, would work.
Syrian officials have said they will make no concessions at the negotiating table. Opposition figures have complained that they are being forced into the talks.
Kerry said those recent statements reflect only "tensions" and "rumors." He dismissed suggestions of disunity among countries that back the opposition and said US support for foes of Syrian President Bashar Assad remains solid.
"I think these are just tensions. These are things you hear as people are worried," he said.
"We are not going to give today what we did not give over the past five years," Hilal al-Hilal said late Saturday, during a visit to troops in areas they recently captured from insurgents outside the capital, Damascus.