"It's going to be very ambitious," Singer told IGN.com. "It's called 'Days of Future Past.' It deals with aspects of that comic, but also some very new things -- I just don't want to give any of it away."
The classic 1981 story by Chris Claremont and John Byrne, which appeared in "The Uncanny X-Men" #141-142, depicts a timeline created by the X-Men's failure to prevent the Brotherhood of Evil Mutants from assassinating a U.S. senator. In that alternate future, the giant robotic Sentinels have become the de facto rulers of the United States, where mutants are hunted down and placed in internment camps.
Singer acknowledged that the sequel, again directed by Matthew Vaughn, could significantly expand the on-screen world of the X-Men while strengthening ties to the rest of the franchise.
"I think there's a strong desire to broaden out the universe," he said. "I mean, the X-Men Universe is every bit, on its own, as big as the Marvel Universe, and I think it's time to reach out and explore it, and perhaps even bring some connectivity between the films -- as Marvel has done so well."
"X-Men: Days of Future Past" opens July 18, 2014.