What is the fine-grained topic of the following text: Iranian top diplomat further explained, 'ten years ago, Bolton introduced policies against uranium enrichment, but in the end Iran managed to increase the number of centrifuges to 20,000 in the next ten years, while we only had 200 centrifuges back then. Only return the topic.
The fine-grained topic of the text is "Iran's increase in uranium enrichment and centrifuges over the past decade".