President Volodymyr Zelensky said on Thursday that he had discussed with European leaders the possibility of sending European peacekeeping forces to Ukraine as part of a cease-fire or peace deal, as the country’s allies consider options on how to help Kyiv end the fighting with Russia on favorable terms.

But the Ukrainian leader added that deploying peacekeepers would not be enough to ensure the country’s long-term security, and that only NATO membership could secure Ukraine against future Russian attacks.

“As long as Ukraine is not in NATO, this aspect can be considered,” Mr. Zelensky said of the peacekeeper idea, after a meeting with European counterparts in Brussels.

The notion of peacekeepers has been greeted with skepticism in several European capitals; Mr. Zelensky said no decision had yet been taken on sending them, and emphasized that any such move would require careful consideration.

“If we’re talking about a contingent, we need to know specifically how many, what they will do, and how they will respond if there’s aggression from Russia,” he said. “There’s a lot to consider. We are discussing this topic. It’s important that we raise these issues.”

His remarks came at a meeting of European leaders at a one-day summit to discuss several issues, including Europe’s relationship with the United States and the need for stability in Syria. The question of how European countries could step up support for Ukraine in Russia’s war dominated the discussions.