The source described political discussions as tense but said the military track generated cautious optimism.
A main focus was agreeing on core terms — such as practical ceasefire conditions and what would constitute a violation — to feed into political talks.
Progress was made in this area, though political leaders must still approve it. The next meeting could occur in the coming weeks.
The two-day talks ended on Feb. 18.
Ukrainian President Volodymyr Zelenskyy called them difficult, with progress limited to military issues, including U.S.-monitored ceasefire mechanisms.
Axios reported a deadlock due to Russia’s position, while U.S. special envoy Steve Witkoff cited substantial progress.
Head of Ukraine’s Presidential Office Kyrylo Budanov described the talks as tough but important, adding preparations were underway for continuation soon.
Russian delegation head Vladimir Medinsky called them businesslike.