They are 7.62x25, also known as the 7.62 or .30 Tokarev. They are dimensionally identical to the 7.63 or .30 Mauser, but should not be fired in the older pistols.
The caliber was the standard Soviet, Chinese and Korean pistol and SMG caliber at that time. They are maybe Russian, but probably Chinese. I don't think the North Koreans had any ammunition plants at that time.
Jim
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