Final answer:
The Soviet Union opposed and did not agree to the U.S. proposal for an international atomic agency to supervise atomic raw materials, leading to the end of efforts for nuclear arms control by the Baruch Plan.
Step-by-step explanation:
The Soviet Union's response to the United States' proposal for an international atomic agency was one of opposition and distrust. After Truman's advisor, Bernard Baruch, presented the Baruch Plan to the UN Atomic Energy Commission, the plan was met with strong resistance from the Soviet Union. The Soviets took a stance that they would only discuss international controls on atomic weapons if the U.S. agreed to destroy its atomic weapons first. This standoff ended the efforts to control nuclear arms through the Baruch Plan during that time. The Soviet Union's desire to bolster its own security and technological advancement was in direct conflict with U.S. attempts to manage and control the spread of nuclear weapons. Eventually, the early testing of a Soviet atomic weapon ended the United States' monopoly on nuclear technology.