From the Electronic Telegraph, 1997:
Yet she [JK Rowling] says that fantasy doesn't greatly appeal to her.
"I don't read it; and it feels odd to speak of what I've written as fantasy. It's all set obviously in a very fantastical context, but some of the characters I think we've all met. Harry has no parents to love; his affections and loyalties are to his friends, but there are adults around who he feels might be his parents. I'm far more interested in those ideas."
From the Australian, 1998:
These days well-meaning people give Rowling fantasy books to read. But she prefers Jane Austen and Roddy Doyle. "Fantasy is not my favourite genre. Although I love C. S. Lewis, I have a problem with his imitators."
From the Newsweek, 2000:
"In fact, I don't really like fantasy. It's not so much that I don't like it, I really haven't read a lot of it. <...> It didn't occur to me for quite a while that I was writing fantasy when I'd started "Harry Potter," because I'm a bit slow on the uptake about those things. I was so caught up in it. And I was about two thirds of the way through, and I suddenly thought, This has got unicorns in it. I'm writing fantasy!"
From AOL Live Chat, 2001:
Q: Why did you focus on magic?
JKR: It chose me. I never really sat down & thought 'what shall I focus on' and in fact, I don't really read fantasy; it's not my favourite genre.
Interview with Steven Kloves, who wrote Harry Potter film scripts, Written By, 2001:
"I confessed to Jo right away that I wasn't a fan of fantasy," he says. "She said, 'Relax, neither am I.'"
For 2005, apart from The Times article mentioned above, there is a transcript of ITV press conference where she says:
JK Rowling: That is one thing I can definitely rule out I don't think I will write any more fantasy books. The reason for that, obviously I have now written a huge long fantasy which will be longer when it is finished and I think I have really put my best fantasy ideas into Harry Potter and if I try to write another fantasy I would feel it was second best. And I love the characters I have written in Harry Potter so much, maybe it will feel like a slight betrayal if I did a second fantasy. I would like to just, that to be my one and only brave stab at that genre, I think.
alt.fan.harry-potter, in which Pratchett himself (under "pterry" which is his handle in Usenet) dropped a few comments. I'm too lazy to search that for you, but if you're interested you should easily find it, and it should contain references to what you're looking for.