Russian Foreign Minister Sergei Lavrov on Wednesday said sending peacekeepers to Ukraine could lead to a direct confrontation between Russia and the NATO military alliance.
Poland said last week that it would formally submit a proposal for a peacekeeping mission in Ukraine at the next NATO summit.
"I hope they understand what they are talking about," Lavrov told staff and students at the Moscow State Institute of International Relations.
"This will be the direct clash between the Russian and NATO armed forces that everyone has not only tried to avoid but said should not take place in principle."
Moscow has accused Kyiv of stalling peace talks by making proposals unacceptable for Russia. Ukraine has said it is willing to negotiate but will not surrender or accept Russian ultimatums.
Lavrov said Ukrainian authorities were backing away from their own proposals at the talks, making it difficult to achieve a breakthrough.
"The talks have started, they are difficult because the Ukrainian side... constantly changes its mind and backs away from its own proposals," Lavrov said.
Ukrainian President Volodymyr Zelensky said earlier on Wednesday that the talks with Russia were tough and at times confrontational.
Russia sent tens of thousands of troops into Ukraine in what it called a special operation to degrade its southern neighbor's military capabilities and root out people it called dangerous nationalists.
Ukrainian forces have mounted stiff resistance and the West has imposed sweeping sanctions on Russia in an effort to force it to withdraw its forces.
