The ongoing battle over Mitt Romney's personal income tax returns isn't personal, President Barack Obama said Monday, saying instead it was essential for voters to understand a presidential candidate's financial background.

Speaking in the White House Briefing Room, Obama pointed to a precedent on releasing tax returns that extended back to Romney's father, George, who ran for the GOP presidential nomination ahead of the 1968 election.

"When it comes to releasing taxes, that's a precedent that was set decades ago, including by Gov. Romney's father," Obama said. "And for us to say that it makes sense to release your tax returns as I did, as John McCain did, as Bill Clinton did, as the two President Bushes did, I don't think it's anyway out of bounds."

Romney released his 2010 income tax return and an estimate of his 2011 return when he filed for an extension. He has vowed to release his full 2011 information once it's completed by his accountant.

Democrats say two years of income tax information isn't enough for voters to assess a presidential candidate, and have pressured Romney to release more. Last week Obama's campaign manager said if Romney released an additional three years of tax returns - making five years total - the Obama campaign would stop pushing Romney to release more.

Also last week, Romney told reporters at a press conference that he's paid an effective tax rate of 13% for the past decade, calling the interest in his tax returns "very small-minded compared to the broad issues that we face."

On Monday, Obama said voters expected more disclosure from presidential candidates.

"I think people want to know that everybody's been playing by the same rules including those who are seeking the highest office of the land. This is not an entitlement being president of the United States. This a privilege and we've got to put ourselves before the American people to make our case," Obama said.

He later added that the calls for Romney to release more taxes were not making personal attacks on the presumptive GOP nominee.

"This isn't overly personal, guys," Obama said. "This is pretty standard stuff. We're not being mean."