US Democratic front-runners Hillary Clinton and Barack Obama have traded accusations over a photo of Mr Obama circulating on the internet.
The picture, sent to the Drudge Report website, shows Mr Obama wearing traditional African dress during a visit to Kenya in 2006.
The Obama camp said it was circulated by Mrs Clinton's staff as a smear. Mrs Clinton's team denied the accusation.
The row comes as the rivals campaign for two crucial primaries next week.
Analysts say Mrs Clinton needs to win the contests, in Texas and Ohio, to remain in the race to choose the Democratic candidate for November's presidential election.
'Fear-mongering'
The photograph shows Mr Obama - whose father came from Kenya - wearing a white turban and a white robe presented to him by elders in the north-east of the country.
According to the Drudge Report, which published the photograph on Monday, it was circulated by "Clinton staffers".
Some Clinton aides have tried in the past to suggest to Democrats that Barack Obama's background might be off-putting to mainstream voters.
A campaign volunteer was sacked last year after circulating an email suggesting, falsely, that Mr Obama was a Muslim.
But the BBC Justin Webb in Ohio says the photograph - coming at this pivotal moment in the campaign - is being seen by the Obama team as particularly offensive.
His campaign manager, David Plouffe, accused Mrs Clinton's aides of "the most shameful, offensive fear-mongering we've seen from either party in this election".
The accusation was dismissed by Mrs Clinton's campaign manager Maggie Williams.
"If Barack Obama's campaign wants to suggest that a photo of him wearing traditional Somali clothing is divisive, they should be ashamed," she said.
"Hillary Clinton has worn the traditional clothing of countries she has visited and had those photos published widely."
Mrs Williams did not address the question of whether staffers circulated the photo.
