The Vatican is part of a peace mission to end the war in Ukraine, Pope Francis said Sunday.

“The mission is in the course now, but it is not yet public. When it is public, I will reveal it,” Francis told reporters.

The pontiff made the remarks as he returned to Rome following a three-day trip to the Hungarian capital, Budapest.

During his visit, Francis met with a representative from the pro-Kremlin Russian Orthodox church, Metropolitan Hilarion, and separately with Hungarian Prime Minister Viktor Orbán.

Asked if the meetings could accelerate peace, Francis said: “I believe that peace is always made by opening channels; peace can never be made by closure.”

Also asked if he was willing to help facilitate the return of Ukrainian children taken to Russia, the pope said: “The Holy See is willing to act because it is right, it just is.”