Military officials participating in trilateral negotiations with Ukraine, Russia and the United States have made “incremental but significant progress” in determining how the ceasefire will work, including finalizing key conditions and clarifications that lay the groundwork for a future agreement, a person familiar with the negotiations told CNN on Wednesday.

The official said that although political negotiations remain “tense,” military negotiations have left officials feeling cautiously optimistic.

The past two days of military-to-military talks were held in Geneva alongside political negotiations led by U.S. Special Envoy Steve Witkoff and Jared Kushner, and led by U.S. Army Secretary Dan Driscoll and U.S. European Command Commander Gen. Alex Grynkewich.

One of the main tasks of military negotiations was to obtain agreement from both sides on key terms to be used in political negotiations, including the substantive terms of a ceasefire and what constitutes a violation of the ceasefire. Although progress has been made on this front, political authorities still need to give final approval, the official said. Officials expect another meeting to be scheduled in the near future, possibly within the next few weeks, the people said.

The political interpretation of the talks struck a different tone. Ukrainian President Volodymyr Zelenskiy said on Wednesday that the results of the talks were unsatisfactory.

“Military representatives seriously and substantively discussed certain issues,” Zelenskiy said. “However, sensitive political issues, the possibility of compromise, and the necessary summit meeting have not yet been fully resolved.”

Vladimir Medinsky, the presidential adviser who led the Russian delegation, said the political negotiations were “difficult but administrative.”