Barack Obama was criticised after his speech was published on the internet
Democratic presidential hopeful Barack Obama has said remarks about "bitter" working-class people "clinging to guns or religion" were ill-chosen.
After a storm of criticism from his rivals, Hillary Clinton and Republican John McCain, Mr Obama said he "didn't say it as well as I should have".
He made the contentious remarks at a fundraiser in San Francisco on Friday.
The Illinois senator is ahead of Mrs Clinton in terms of delegates won in the Democratic primaries so far.
Mrs Clinton is hoping to reduce his lead when Pennsylvania holds its key primary election on 22 April.
However, the majority of polls published last week suggested Mrs Clinton's lead in the state had narrowed to the low single digits.
'Out of touch'
Mr Obama was accused of taking a condescending view of small-town voters after he was filmed at the private fundraising gathering last weekend, during which he said he understood why residents of some hard-pressed communities grew angry.
"You go into these small towns in Pennsylvania and, like a lot of small towns in the Midwest, the jobs have been gone now for 25 years and nothing's replaced them," he said.
"And it's not surprising, then, they get bitter, they cling to guns or religion or antipathy to people who aren't like them or anti-immigrant sentiment or anti-trade sentiment as a way to explain their frustrations," he added.
Mrs Clinton said her rival's comments had been condescending and suggested voters in Pennsylvania did not "need a president who looks down on them".
"I was taken aback by the demeaning remarks Senator Obama made about people in small-town America," she said on Saturday.
"Senator Obama's remarks are elitist and are out of touch. They are not reflective of the values and beliefs of Americans, certainly not the Americans that I know."
Mrs Clinton said the remarks did not reflect the values and beliefs of voters
An adviser to Mr McCain, Steve Schmidt, said his candidate believed the statement was "nothing short of breathtaking", and that it was "hard to imagine someone running for president who is more out of touch with average Americans".
At a rally in Indiana on Saturday, Mr Obama conceded his description had been clumsy and not conveyed its intended meaning.
He said he believed many voters were indeed bitter about the economy and that he had meant to say that "when you're bitter you turn to what you can count on".
"So people - they vote about guns, or they take comfort from their faith and their family and their community," he said, adding that it was a "natural response".
"The truth is that these traditions that are passed on from generation to generation, those are important. That's what sustains us."
The latest count of pledged delegates to the party's national convention in August, according to the Associated Press, gives Mr Obama the support of 1,638 delegates and Mrs Clinton 1,502.