Republican presidential candidate Ted Cruz decided to run for president after he felt the Holy Spirit urging him to do so during an intense prayer session, his father, Pastor Rafael Cruz revealed.

Speaking on Dove TV recently, the elder Cruz said at the culmination of six months of prayer, the family held a two-hour prayer session where his son Ted felt the presence of the Holy Spirit in the room, Raw Story reported.

"We all were at awe," Rafael Cruz said. "And Ted, all that came out of his mouth, he said, 'Here am I Lord, use me. Here am I Lord, I surrender to whatever Your will for my life is.' And it was at that time that he felt a peace about running for president of the United States."

Ted Cruz won the Iowa caucus on Monday night, upsetting Donald Trump, who had led in pre-caucus polls and even in Monday's exit polls.

Rafael Cruz also spoke to WND to explain further his son's motivation in seeking the highest office in the land.

"For many years, the church has been absent from the political process," he said. "Surveys that [Christian pollster] George Barna has done show that nearly half of all evangelicals don't even vote. So when that happens, of course, you're going to have a situation where too many people say, 'Politics is a dirty business, I don't want a part of it.'

"But if the people of principle don't vote and don't run for office," he asked, "what is left? People without principle voting for people without principle, and we get what we deserve."

Rafael Cruz said his son defied the polls and pundits to win the first contest in the Republican primaries by "empowering the faithful."

"What I think is happening is the sleeping giant is waking up," he said. "What we are seeing are millions and millions of conservatives, of evangelicals, beginning to wake up. And I think the catalyst for that was the June 26, 2015, Supreme Court decision that tried to redefine marriage. Because it was much more than that; it was a direct frontal attack on religious liberty."

The GOP candidate's father said he believes the action taken by the Supreme Court galvanised Christians to make their presence felt in this year's election.

He said this explains the record turnout in the Iowa GOP caucuses. His son appealed strongly to these voters, emphasising that he shared their values.

"The Body of Christ is waking up, and they are coalescing around my son," he said.