GOP front-runner Mitt Romney speaks to reporters after a campaign stop at McCandless Trucking in North Las Vegas, Nev., on Friday. (Charles Dharapak/AP)

NORTH LAS VEGAS, Nev. — Mitt Romney on Friday pushed back forcefully against Senate Majority Leader Harry Reid’s claim that, according to an unnamed source, there were several years during which the presumptive GOP nominee did not pay taxes.

“Let me say categorically, I have paid taxes every year — a lot of taxes,” Romney said during a brief news availability after a campaign event at a trucking company warehouse. “So Harry is wrong.”

He also doubled down on his response to Reid (D-Nev.) from earlier in the week: “Harry Reid really has to put up or shut up. So Harry, who are your sources?”

The pushback from Romney comes as Democrats — including Reid, the top Democrat in the Senate — have been seeking once again to pressure Romney to release more than two years of his tax returns.

Senate Majority Leader Harry Reid (D-Nev.) (Kevin Lamarque/Reuters)

Outside the North Las Vegas event, about two dozen protesters were gathered in the 90-degree heat, urging Romney, “Show us your taxes! Show us your taxes!”

Among those gathered outside the event to hammer Romney on the tax issue was Joe King, 54, a self-described Democrat from Las Vegas who is currently unemployed.

Clad in a gray tank-top, shorts and a Bally’s visor, he held up a sign reading: “Mitt wants a new federal address? How about a federal penitentiary for tax fraud?”

“Obviously, I think he should be in prison,” he said of Romney. “He’s a tax evader; anybody stashing away money like that, he doesn’t believe in America.”

Friday marked the first time that Romney himself had stated that there was never a year during which he owed nothing in taxes. Romney aides have previously stated as much.

But Romney still faces lingering questions over how much he did pay in taxes in years before 2010. Romney said in an interview last month with ABC News that he could not recall and would have to check to see whether there was a year when he paid less than the 13.9 percent rate he paid in 2010.

The North Las Vegas event also marked Romney’s first news availability since returning to the United States from his foreign trip; it comes as relations between his campaign and the media have come under strain.

On his foreign trip, Romney appeared at a news event in London but answered questions only from British reporters, not his traveling press corps. Reporters, frustrated that Romney had answered only three questions during the trip, shouted queries at him at an event in Poland last week but received a sharp retort from a traveling press secretary.

Romney’s western trip appears in some aspects an effort to repair relations with the media as the campaign heads into the pre-convention weeks.

On Thursday, Romney, clutching a McDonald’s bag, briefly chatted with reporters at the back of his plane. On Friday, campaign aides unfurled a happy birthday banner for an Associated Press photographer upon arriving in Las Vegas, and Romney posed for a birthday photo with the photographer, Charles Dharapak.

The Friday press availability was dominated by questions related to taxes — both Romney’s and the Bush-era tax cuts — as well as to the economy more broadly.

In a response to a reporter’s question on impending defense cuts and tax reform, Romney called for a year-long extension of the current rates in order to give the next president “the capacity to reform our tax system.”

He also denounced as “patently untrue” the argument by Obama and others that his economic proposals would lower taxes on higher earners.

“Higher-income people are not going to pay a smaller share of taxes in America if I’m president,” he said, pushing back on Democratic arguments as well as a new nonpartisan report to the contrary.

“I will not raise taxes on the American people. ... The president and his campaign’s assertions to the contrary are simply false,” he said.

Asked about the recent debates over Chick-fil-A and same-sex marriage as well as claims by Rep. Michele Bachmann (R-Minn.) and others that State Department aide Huma Abedin is in league with the Muslim Brotherhood, Romney declined to weigh in.

“Those are not things that are part of my campaign,” he said.

And he told reporters that he “absolutely” plans to announce his running mate before the GOP convention in Tampa wraps up.

Several potential running mates, including Louisiana Gov. Bobby Jindal and New Jersey Gov. Chris Christie, appeared alongside Romney at a Basalt, Colo., event Thursday night.