Newt Gingrich has thanked his main campaign donors after announcing his exit from the Republican presidential primary race.

Mr Gingrich paid tribute to Sheldon and Miriam Adelson, who gave an estimated $20 million to a political action committee that supported the former House Speaker.

Mr Adelson, a Jewish casino billionaire and prominent philanthropist, was in 16th place on the 2011 Forbes list of the world's billionaires.

In a farewell address, Mr Gingrich said: "Of course, while they weren't directly associated with the campaign, it would be impossible for me to be here without Sheldon and Miriam Adelson, who single-handedly came very, very close to matching Romney's super-PAC. I'm very, very grateful."

Mr Adelson is likely to shift his support to the presumptive Republican nominee, Mitt Romney. But speaking last month, he said Mr Romney, was "not the bold decision maker like Newt Gingrich is".

Despite Mr Adelson's support for the Republican candidates, a survey published this week confirmed that the tendency of Jewish voters to back the Democratic Party remained in place.