The names, attributed to Republicans close to the campaign, were reported by The Washington Post Wednesday, a day after Romney, the presumptive Republican presidential nominee, told reporters in Holland, Mich., his vice-presidential search team was vetting U.S. Sen. Marco Rubio of Florida, one of the Republican Party's biggest young stars.
"Marco Rubio is being thoroughly vetted as part of our process," Romney said, denying an ABC News report to the contrary.
Romney's denial came the same day a book, "The Rise of Marco Rubio," was published by Simon & Schuster.
The book, written by Washington Post writer Manuel Roig-Franzia, says Rubio has been called the "crown prince" of the Tea Party movement and "the Michael Jordan of Republican politics."
The Romney campaign had no immediate comment on the coincidental timing.
Rubio, 41, was born to Cuban immigrants and raised in Miami and Las Vegas. He was elected to the Senate in 2010 after serving as speaker of the Florida House of Representatives.
On Oct. 5, 2011, he told the Fox News Channel he would turn down a vice-presidential spot.
"I'm not going to be the vice-presidential nominee. ... I'm focused on my job right now. ... The answer is going to be no," he said.
Rubio had no immediate comment after Romney said the senator was being vetted.
"There was a story that originated today, apparently at ABC, based upon reports of supposedly outside unnamed advisers of mine," Romney told reporters at an impromptu briefing Tuesday. "I can't imagine who such people are. But I can tell you this -- they know nothing about the vice-presidential selection or evaluation process.
"There are only two people in this country who know who are being vetted and who are not, and that's Beth Myers and myself. And I know Beth well. She doesn't talk to anybody. The story was entirely false," Romney said.
Myers is a senior Romney campaign adviser who is in charge of the running-mate search.
A few hours before denying the ABC report, Romney laughed it off.
"I get a kick out of some of the speculation that goes on," he told Fox News. "I'm not going to comment on the process, of course. But I can tell you this -- only Beth Myers and I know who is being vetted."
Portman, 56, joined Romney in Ohio Sunday during Romney's five-day tour of small towns and rural areas in New Hampshire, Pennsylvania, Ohio, Wisconsin, Iowa and Michigan. Portman was cited as a potential running-mate for 2008 Republican presidential nominee John McCain.
Pawlenty, 51, a Republican presidential hopeful from May to August 2011, joined Romney on the bus tour in New Hampshire and Pennsylvania. Pawlenty, who endorsed Romney in September 2011, was a runner-up to be McCain's running-mate. He remained closely involved with McCain's presidential bid.
Romney's denial of the report was widely seen as a rare breach of his secretive process for selecting a running-mate.
2014: The Year in Music [PHOTOS]