It's the topic Republican presidential candidate Mitt Romney wishes would go away – but it won't. On Thursday, Romney tried to keep the focus on Medicare, but questions about his taxes just kept coming. NBC's Ron Mott reports.

Updated 12:41 p.m. - GREER, S.C. -- Mitt Romney said Thursday that he had never paid less than a 13 percent effective tax rate after reviewing his returns from the past decade.

The presumptive Republican presidential nominee did not pledge to release any additional returns beyond what he had previously pledged, but essentially quashed rumors that he paid no taxes at some point.

Evan Vucci / AP Republican presidential candidate Mitt Romney arrives at Birmingham International Airport, Ala., before boarding a plane for fundraising events Aug. 16.

"Given the challenges that America faces -- 23 million people out of work, Iran about to become nuclear, one out of six Americans in poverty, -- the fascination with the taxes I paid I find to be very small-minded compared to the broad issues we face," Romney told reporters gathered for a press conference at the Greer airport in South Carolina, where Romney had just arrived to attend a fundraiser.

"I did go back and look at my taxes, and, over the past 10 years, I never paid less than 13 percent," he said, later adding: "Every year, I paid at least 13 percent, and if you add in, in addition, the amount that goes to charity, the number gets well above 20 percent."

The wife of presidential candidate Mitt Romney defends their decision to not release tax forms from before 2010, and has some surprising words to say about the Obama family. NBC's Natalie Morales reports.

But the former Bain Capital executive has been dogged by accusations -- principally from Senate Majority Leader Harry Reid (D-NV) -- that he had skirted paying taxes.

"Harry Reid's charge is totally false. I'm sure waiting for Harry to put up who it was who told him what he says they told him. I don't believe him for a minute, by the way," Romney said.

Romney has released his tax returns from 2010, which reflected that he paid a 14 percent effective tax rate. This was because most of his income came from investments, which are taxed at a lower rate than employment income.

Democrats have highlighted the discrepancy between investment and employment income in making their case for comprehensive tax reform in which the wealthiest Americans would face a higher tax burden.

The former Massachusetts governor has vowed to make public his 2011 tax returns before Election Day, but Romney has strenuously resisted making any of his other returns public.