WASHINGTON (AFP) - Republican US House speaker Paul Ryan ruled out a late run for the presidency on Tuesday (April 12), squelching speculation that he could be in contention at an eventual contested party nominating convention in July.

"I made a really clear choice not to run for president. Therefore, I will not be nominated," Ryan told a radio talk show host in his home state of Wisconsin.

"It will not be me. I don't know how I can be clearer than that," Ryan said in the interview, parts of which were aired by MSNBC.

Later, he told reporters on Capitol Hill: "Count me out."

Current Republican frontrunner Donald Trump has a healthy lead over his closest rival Senator Ted Cruz, who is trying to deny the billionaire the delegates needed for an uncontested nomination at the Republican party convention in Cleveland in July.

If no one has the 1,237 delegates needed to win the nomination outright, the candidates head to a contested convention where - if the initial vote produces no winner - delegates would be unbound for subsequent ballots and allowed to vote for whoever they want.

Trump has complained bitterly that the Republican establishment is seeking to block him from the nomination and has agreed to back Cruz as a way to do so.

Some have speculated that Ryan, the 2012 vice presidential nominee, could step forward, despite his repeated dismissals of the idea.

On Tuesday, he again said that delegates should choose a nominee from "among the people who actually ran for president this year."

"We have too much work to do in the House to allow this speculation to swirl or to have my motivations questioned," Ryan said.

"I should not be considered - period, end of story."