Republican presidential candidate Marco Rubio has said that he will fight for an America where no one has to violate their conscience and everyone has a right to believe what they want.

Speaking in Iowa on Monday, Marco was asked a question by Justin Scott, an atheist from Waterloo, on his recent advert, which focussed on the Republican candidate's faith rather than policy.

Scott said that atheists – and non-theists – are "looking for somebody that will uphold their rights as Americans, and not pander to a certain religious group."

To this, Rubio said: "You have a right to believe whatever you want, and I congratulate you on believing whatever you want."

Emphasising this point, he went on to say: "I can't force you to be a Christian. Christianity is a free gift. We believe that salvation is a free gift that has to be wilfully accepted."

He said he would champion a nation in which "no one is forced to violate their conscience – which means no one is going to force you to believe in God, but no one is going to force me to stop talking about God."

Rubio, whose Roman Catholic faith has become a prominent feature of his campaign, unapologetically said his faith "is the single greatest influence in my life", but that it's not something to be feared by atheists.

"I am not going to force you to pray, I am not going to force you to go to church, I am not going to force you to espouse beliefs you don't have," he said.

"But no one is going to take away my right or your right to live out the teachings of your faith. No one."

Rubio added that rather than fearing that his faith may influence his politics, Scott should hope for it, as it is the very driving force behind his concern for the less fortunate, the hungry, and those in prison.

Commending Scott for asking the question, Rubio said: "I respect very much your willingness to stand up and ask that question because I know that you are a small minority here that share that view, but you have a right to, and that is what makes this such a great country."

Just 12 days before the Iowa caucus, Rubio is currently holding third place in the state according to the polls-plus model, with 13 per cent of the vote. Ted Cruz is leading the poll with 51 per cent, followed by Donald Trump with 29 per cent.