Am I being rude, or are my friends?

Well I like to have long conversations with my friends. Lets say I have a long talk with a friend, and another friend interrupts me while I am talking with a different friend already. I turn around and say "Hi, hold on." to the person who is interrupting me. Then the friend that interrupts me says... show more Well I like to have long conversations with my friends. Lets say I have a long talk with a friend, and another friend interrupts me while I am talking with a different friend already. I turn around and say "Hi, hold on." to the person who is interrupting me. Then the friend that interrupts me says "Gosh, you are so rude!". I don't get how that is rude. Is it? But I am trying to talk with a friend that I was talking with before her!!. My friend was talking to me and my other friend interrupts.

I am asking this because it has been happening frequently with two of my friends. They always interrupt me. Interrupting is rude, I know that, but am I rude by saying "Wait a second!" or "Hold on just a minute!"?? If it is rude, how should I handle talking with one friend, and talking to the other, without making my friends angry and thinking I am rude?? If I am not rude, what should I say to them to tell them that they are the ones being rude?
Update: I always have a nice tone in my voice by the way, unless someone doesn't have a nice tone with me or something upsets me. That is my strategy.
Update 2: Thank you so much guys for your wonderful answers! I didn't expect to get that many answers, and all that aren't silly ones either. And Bernard yes my friends easily get offended, when some say that I do?? Maybe sometimes, but not as badly as them.
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