Is a referendum on territories possible during wartime?

I read that President Zelenskyy said that issues concerning territories mentioned in the peace plan should be decided by the people — either through elections or a referendum. However, a war is currently ongoing, martial law is in effect, and large territories are under occupation. I am interested: is it really possible to hold a referendum or elections on such an issue during martial law, and will such a decision be legally valid if not all citizens can participate? How can this work in practice under current conditions?