The Cold War enemies have been trying to broker a new truce after a ceasefire agreed in February unravelled in weeks, with the US accusing Syrian President Bashar al-Assad's forces - which are backed by Russia - of violating the pact.
US President Barack Obama described his talks with Russian counterpart Vladimir Putin as tough but productive after their meeting at the G20 summit in China.
Putin said they had understood each other and that an agreement on ways to reduce the violence in Syria could be reached in days.
"We have had some productive conversations about what a real cessation of hostilities would look like, that would allow us both, the US and Russia, to focus our attention on common enemies, like [Islamic State] and the Nusra [Front]," Obama said.
"We haven't yet closed the gaps [in agreeing on a Syria policy]," he said, but added that his secretary of state, John Kerry, and Russian Foreign Minister Sergei Lavrov, would "keep working at it over the next several days".
Putin told journalists that it was premature to give details about the terms of the agreement, but that the two nations would strengthen co-operation in fighting terrorism.
Truce talks were complicated on Sunday as government forces and their allies laid siege to the rebel-held eastern side of Aleppo, Syria.
Assad's gains have relied heavily on Russian air support.
Six bomb blasts yesterday hit the west of Damascus and in the government-held cities of Homs and Tartous, as well as in the Kurdish-controlled province of Hasaka, state media and a monitoring group said.
IS carried out the suicide attacks, it said yesterday.
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