Mitt Romney filed an extension on his 2011 tax returns, his campaign announced on Friday.

The Romney campaign said that the extension is routine and he files one every year.

The campaign's announcement came late Friday afternoon, the same day the White House released tax returns for President Obama and Vice President Biden. Obama's reelection campaign urged Romney to release more of his tax returns.

"Sometime in the next six months, and prior to the election, Gov. Romney will file and release the 2011 return when there is sufficient information to provide an accurate return," campaign spokeswoman Andrea Saul said in a statement.

The 2011 extension shows that Romney estimated his total tax liability to be $3.2 million. With the extension he paid an estimated tax of $887,000.

Romney faced a great deal of criticism during the Republican primary process for not releasing his returns. In February, he released his 2010 tax return and an estimate for 2011.

His wealth — which he has said is between $190 million and $250 million — has been a campaign issue.

Democrats hope to use it to paint Romney as out of touch with middle-class Americans and push the "Buffett Rule," legislation which would raise income taxes for the richest Americans.

Romney has said that his 2010 tax returns and 2011 estimate were sufficient and he would only release more when it was necessary. 

— Last updated at 5:47 p.m.