US presidential hopeful Barack Obama has sought to tackle the issue of race and defuse a controversy over comments made by his former pastor.
Senator Obama said he understood the history of anger between black and white Americans but that the US could not afford to ignore race issues.
He referred to the uproar over what he called the Rev Jeremiah Wright's "profoundly distorted view" of the US.
Mr Wright said the 9/11 attacks were like "chickens coming home to roost".
After the remarks resurfaced, Mr Obama denounced them as "incendiary" and "completely inexcusable" and said he had not been present when they were made.
Mr Obama is locked in a close race with New York Senator Hillary Clinton for the Democratic nomination, with the significant Pennsylvania primary vote due on 22 April.
The BBC's Jamie Coomarasamy in Philadelphia says this was a bold speech with considerable risks, but one which Barack Obama clearly felt he had little choice but to make to defuse the race issue.
Speaking in Philadelphia, the Pennsylvania city seen as the cradle of US democracy, Mr Obama referred to America's long history of racial inequality - and called on the US to move beyond it.
"The anger is real; it is powerful; and to simply wish it away, to condemn it without understanding its roots, only serves to widen the chasm of misunderstanding that exists between the races," he said.
As the child of a black father and white mother, he said he understood the passions of both sides in what he called "a racial stalemate we've been stuck in for years" - and said he was not so naive as to believe it could be overcome in one election cycle.
However, Mr Obama said, he believed the nation could - if it worked together - move towards healing some of the wounds caused by racial injustice.
And while he condemned many of Mr Wright's political views as "not only wrong but divisive", he pointed out that the pastor had grown up at a time of racial segregation.
"I can no more disown him than I can disown the black community. I can no more disown him than I can my white grandmother," he said.
He recalled that his grandmother had raised him and loved him - but that at times she had used racially-tinged language or stereotypes that made him "cringe".
'Don't walk away'
Mr Obama also said that it should not be surprising to Americans that anger over racial injustice still finds voice in many black churches.
The row was sparked by sermons given by the Rev Jeremiah Wright
He challenged the nation not to ignore the issue of race "this time" - while acknowledging that white Americans, especially the working class, also had their problems.
"If we walk away now, if we simply retreat into our respective corners, we will never be able to come together and solve challenges like health care, or education, or the need to find good jobs for every American."
Race has emerged as an issue on several occasions in the battle between Mr Obama and Hillary Clinton for the Democratic presidential nomination, but at no time before has Mr Obama addressed it so directly.
Former President Bill Clinton was accused of stirring up racial tensions over remarks he made after Mr Obama's victory in South Carolina's primary in January, in which he seemed to try to marginalise Mr Obama as a black candidate winning a state with a heavily black electorate.
In an interview with US network ABC broadcast on Monday, Mr Clinton rejected that criticism, saying it was a "myth" that the Clinton campaign had engaged in racial politics.
Last week, former vice-presidential nominee Geraldine Ferraro resigned from her unpaid advisory post to the Clinton campaign after a row over remarks appearing to suggest Mr Obama had only got where he was because of his race.
Mrs Clinton, also campaigning in Philadelphia on Tuesday, told reporters she had not seen Mr Obama's speech.
But, she added: "These are difficult issues and we have seen that in this campaign. Race and gender are difficult issues. And therefore we need to have more discussion about them."
While the Democratic hopefuls competed in Pennsylvania, John McCain - the presumptive Republican nominee - visited Jordan and Israel, a day after meeting US and Iraqi officials in Iraq.
He told reporters that visiting Iraq - his eighth such trip - made it "palpably clear what a mistake it would be if the United States precipitously withdrew our forces".
In Israel, he visited the national Holocaust memorial, Yad Vashem. Before arriving, he said pursuing the Israeli-Palestinian peace process was a "high priority".
''God damn America'
Mr Wright has resigned from an honorary position on the campaign's African-American Religious Leadership Committee, aides to Mr Obama said.
Before his retirement from Trinity United Church of Christ, in Chicago, the pastor helped Mr Obama affirm his Christian faith, officiated at his wedding and baptised his daughters.
Mr Obama said he had looked to Mr Wright for spiritual, not political, guidance.
In a sermon on the Sunday after the attacks of 11 September 2001, Mr Wright suggested that the US had brought the terror attacks on itself through its own foreign policy.
And in a 2003 sermon, he said blacks should condemn the US because of continuing racial injustice, saying: "God damn America for treating our citizens as less than human."