If Chiang had been held captive for a long time or had been killed then China would have seen a large-scale civil war erupt and this would have provided a good opportunity for Japan to realize its ambition of occupying China which would, on a strategic level, have threatened the Soviet Union. This is the main reason why the Soviet Union did not support the holding of Chiang.
因為若蔣長期被拘押或被殺，中國勢將爆發大規模的內戰，為日本提供侵華良機，若日本佔領中國，對蘇俄本身也構成威脅，這是蘇俄不支持扣蔣行動的最重要原因。