Hours after President Barack Obama and Vice President Joe Biden published their 2011 tax returns, Mitt Romney announced he has requested an extension for his own filing.

The presumed Republican candidate for president estimated his tax liability for 2011 at $3.2 million, according to Boston.com. Romney representative Andrea Saul said the Romneys will file their return in the next six months, before the election, when there is sufficient information to provide an accurate return.

The White House published the president's and the vice president's 2011 tax returns as Obama aggressively pushes the so-called Buffett Rule, a policy that promises to increase taxes for Americans who make more than $1 million a year and fix what the president says is a broken tax system.

The White House said it hoped the release of the tax returns would encourage Romney to do the same.

Although the Romney camp already has made public estimates indicating the candidate made more than $20 million in 2011 and vowed the actual return will come out prior to the election, Fox News Channel White House correspondent Ed Henry tweeted that filing an extension serves up [a] softball to Obama's re-election campaign.

Obama aide David Plouffe pressed Romney to release his tax returns for the past 23 years in an interview with Bloomberg shortly before Romney's extension announcement..

So they're [the tax documents are] just sitting somewhere in a box or a vault or something, and they ought to release it, Plouffe said, adding, If he's got nothing to hide, then there's nothing to lose.

After tripping over his words during the South Carolina primary-election campaign while trying to explain why he had not released his tax returns, Romney finally released his 2010 return in January. The documents showed he made $21.7 million in 2010 and paid 13.9 percent in taxes. He made an estimated $20.9 million in 2011, with about 15 percent going toward taxes. Romney made most of his multimillion-dollar fortune at Bain Capital.

According to the Obamas' 2011 tax return, the president and first lady Michelle Obama reported gross income of $789,674, about half of which is the president's salary and about half is from his best-selling books. The Obamas paid $162,074 in federal tax, reflecting a 20.5 percent tax rate, as well as $31,941 in state income tax, because of their residence in Illinois. In 2010, they reported about $1.7 million in gross income.