The two held talks in Geneva to try to find a way of reviving a cessation of hostilities that faltered months ago.
Mr Kerry said they were close, but would not rush into an agreement.
The talks come as the Damascus suburb of Darayya was evacuated after a four-year siege by the government.
After meeting for nearly 10 hours, Mr Kerry said the "vast majority'' of technical discussions had been completed, adding that experts would remain in Geneva to work on the unresolved steps in the coming days.
He stressed that the only way to solve the conflict was through political agreement.
"We want to have something done that is effective and that works for the people of Syria, that makes the region more stable and secure, and that brings us to the table here in Geneva to find a political solution," he said.
Nearly 10 hours of talks were not enough to close the gaps.
It is clear some progress was made, but the question is whether Russia and the United States will ever be able to reach a lasting deal on crucial and complex issues.
One goal is to strengthen their military co-operation in the fight against so-called Islamic State and forces linked to al-Qaeda.
But they, and their Syrian allies, still disagree on which groups are legitimate targets.
They also want the Syrian government and the opposition to accept a truce.
But, on the ground, fighting intensifies with all sides still trying to gain advantage. In the town of Darayya just outside Damascus, rebels were forced to surrender after four years of bombardment and siege.
The government regards these local deals, on its own terms, as a way forward, not talks by outside powers in foreign capitals.
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