The 27th Day (1957)

Five individuals from five nations, including the "Superpowers" (USA, USSR and China), suddenly find themselves on an alien spacecraft. An alien gives each a container holding capsules. No power on Earth can open a given container except a mental command from the person to whom it is given. Each person has been provided with the power of life and death. Any of these individuals has the capability to instantaneously launch the capsules to whatever coordinates he/she chooses, and each capsule will then eradicate all human life within a 3,000-mile radius of its designated location.