(CNN) - Barack Obama's campaign on Sunday stepped up its efforts to portray rival Hillary Clinton as a secretive politician, calling the New York senator a "veteran of non-disclosure."
In a conference call with reporters Sunday afternoon, Obama's top aides implored Clinton to release past tax returns, earmark requests, documents from her husband’s Presidential Library and the list of donors to the Library.
"What is Sen. Clinton hiding and what is lurking in the documents?" Obama Communications Director Robert Gibbs asked on the conference call.
David Axelrod, the campaign's chief strategist, also repeated the campaign's past claim that the New York senator remains to be fully vetted, and suggested Republicans could unearth now unknown details about Clinton.
The Clinton campaign immediately shot back in a conference call of their own later Sunday, saying the Obama campaign is increasingly going negative, despite its message of hope.
"There has been a pattern of him launching personal attacks that we think have not been as fully publicly seen or realized, as we move month to month in this campaign," Clinton chief strategist Mark Penn said.
Clinton Communications Director Howard Wolfson also responded sharply, saying much of the Clinton tax returns over the last several years have been made public already.
"I would point out there are 20 years of the Clinton tax returns in the public record, and as far as I am aware, there is one year of Senator Obama's tax returns in the public record - 2006," he said. "I would ask the Obama campaign if he or they are prepared to release all of his taxes when he was in elected office, so far the answer to that has been no."
- CNN Ticker Producer Alexander Mooney