Upvote:4
I Applied for B1/B2 Visa but my activities mentioned were just tourism (B2). Could that be the possible reason as I applied for both categories?
No. Most people don't even know the difference between B1 and B2 including myself although I kept getting approved for several years. They routinely give out B1/B2 and even if you applied for the wrong category, the consular would very likely have pointed it out.
What could be the actual possible reason for rejecting the visa, I had a travel history (I recently visited UK) as well.
It could be any one of ten thousand different particular reasons. The bottom-line and summary is they don't believe you will return to your home country. Many times there is little method to the madness of US consular officers in issuing visitor visas in particular. Some decision could only be construed as random.
When can I again apply for the visa as they have mentioned that I should any apply again as if my circumstances have been changed significantly!
You really can apply again even tomorrow although rapid application in succession after refusals usually have increasingly lower probability of success.