Newt Gingrich has said President Barack Obama came out for gay marriage because he is beholden to gay millionaires and activists.

Speaking to conservative outlet Newsmax, Gingrich dismissed Newsweek's The First Gay President cover as a clever ploy.

“Contrary to Newsweek's clever cover I think from everything we know he's heterosexual, so I don't think he's gay,” the former GOP presidential candidate said.

On Obama's recent announcement in support of gay marriage, Gingrich said: “Look, he adopted the policy of his most powerful constituents. The fact is the gay caucus, the gay millionaires, gay activists are at the heart of the Obama system, and they had finally gotten tired of his equivocating. So he said what they wanted him to [say].”

“This is a guy who ran for the state Senate in favor of gay marriage, ran for the U.S. Senate against gay marriage, ran in '08 sort of being equivocal, and this year finally said he's for it. I think it does take the flip-flop attack away. I don't quite see how Obama with a straight face now can say that Romney's changed his positions since it's quite clear that in fact on a pretty major issue Obama's changed his position.”

Gingrich warned that increasing support for marriage equality could translate into “a real danger of militant activists trying to in effect eliminate religious liberty.”

Former rivals Michele Bachmann, Rick Santorum and Rick Perry have also knocked the president's new stance.