US House Speaker Paul Ryan, the top Republican in Congress, said Thursday he was not ready to support Donald Trump as the party's presumptive presidential nominee in November's general election.

"I'm not ready to do that yet," Ryan, who was the Republican vice presidential nominee in 2012, told CNN. But he added that he hoped he would be able to support Trump in the future, provided the brash billionaire is able to show leadership in unifying the party.