Why is Russia opposed to NATO peacekeepers in Ukraine?

Russia strongly objects to NATO peacekeepers in Ukraine, considering it part of what they call "the creep of NATO toward its western border." Russian officials have explicitly stated that the presence of armed forces from NATO countries would be unacceptable, even if they operate under different flags such as the European Union or national flags. During recent diplomatic exchanges, Russia made clear that this disguised NATO presence "does not change anything" and remains "unacceptable" to them. This stance reflects Russia's longstanding concerns about NATO expansion near its territory and demonstrates a significant obstacle to potential international peacekeeping solutions in the ongoing Ukraine conflict.