"No one is working on any movie just now...," he continues. "Don't believe everything you read, boys and girls. Especially not online."
But the novelist goes on to admit there is "great enthusiasm" for the idea, adding, "It would be a great way to end".
He adds, "(HBO) are in the TV business, not the feature film business. And those of you with long memories may recall all the rumours about a Sopranos movie... a Rome movie... a Deadwood movie. Rumours is all they were. And that's all this one is too, at least for now."
Martin previously had to distance himself from talk of a Game of Thrones film after he was falsely credited with suggesting the idea.
"I see that this new crop of stories (reports) also raises, once again, the notion of concluding the series with one or more feature films," he posted in January.
"And in some of these stories, once again, this idea is wrongly attributed to me. Let me state, yet again, that while I love this idea, it did NOT originate with me.
"It was a notion suggested to me, which I have enthusiastically endorsed. Sure, I love the idea. Why not? What fantasist would not love the idea of going out with an epic hundred million feature film? And the recent success of the IMAX experience shows that the audience is there for such a movie. If we build it, they will come. But will we build it? I have no bloody idea."
Game of Thrones is due to return to screens for its sixth season next year.
- WENN