DENVER - Mitt Romney stood staunchly opposed to same-sex marriage today, reaffirming his stance shortly after President Obama announced that he now favors gay marriage, drawing a stark contrast between the two men vying for the White House this November.

"I have the same view on marriage that I had when I was governor and that I have expressed many times: I believe marriage is a relationship between a man and a woman," said Romney at an impromptu news conference following a speech in Oklahoma City this afternoon.

"States are able to make decisions with regards to domestic-partnership benefits, such as hospital visitation rights; benefits and so forth of various kinds can be determined state by state," said Romney. "But my view is that marriage itself is a relationship between a man and a woman, and that's my own preference.

"I know that other people have differing views," he added. "This is a very tender and sensitive topic, as are many social issues."

Earlier today, in an exclusive interview with ABC News' Robin Roberts, President Obama announced his decision to support same-sex marriage.

"I've just concluded that, for me personally, it is important for me to go ahead and affirm that I think same sex couples should be able to get married," said Obama.

Before today, Obama had never vocalized his outright support for same-sex marriage and had only supported civil unions, allowing gay couples to enjoy the same rights and benefits that married couples get.

Asked today whether he believed President Obama has changed his mind on the issue, a criticism Romney himself has been plagued with on a variety of topics, Romney stopped short. But he noted reporting that indicated the president changed his mind on the issue.

"I believe that, based upon the interview he gave today on ABC, it said that he had changed his view, but you're a better judge of that than I am," said Romney. "I just saw the reports that he had previously said he opposed same sex marriage and now, according to ABC News, he said that he supports it. So if that's the case you'll have to make that determination on your own."