Why did the United States and the Soviet Union, allies of World War II, fight an air war over Yugoslavia?

during World War II, the United States and the Soviet Union were allies. The two countries fought side by side against German fascism. But in 1944, at the end of World War II, an air war broke out between the United States and the Soviet Union over Yugoslavia. Why did the United States and the Soviet Union break out an air war over Yugoslavia?

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the "accidental collision" of the United States and the Soviet Union

misunderstanding? Or is there another reason?