Kerry spoke before a meeting in Geneva with Saudi Foreign Minister Adel al-Jubeir in stepped-up diplomatic efforts to stop a surge in fighting and salvage UN-led peace talks brokered by the US and Russia on Feb. 27.
Kerry will meet UN envoy to Syria Staffan de Mistura before returning to Washington later in the day.
The Syrian government said Friday it was introducing a temporary "regime of calm", or lull in fighting, in an area around Damascus and Latakia province; but Kerry has made clear a ceasefire brokered by the US and Russia on Feb 27 must also include Aleppo, which has seen the brunt of the increase in fighting.
"We're getting closer to a place of understanding, but we have some work to do, and that's why we're here," Kerry said at the start of the meeting with Jubeir, Reuters reported.