(CNN) - Mitt Romney continued to stress Tuesday that he has no interest in releasing more tax returns, saying it would provide "hundreds of pages" for opponents to "distort" and turn into attacks against his candidacy.
"In the political environment that exists today, the opposition research of the Obama campaign is looking for anything they can use to distract from the failure of the president to reignite our economy," Romney said in an interview with conservative news outlet National Review Online.
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He continued: "And I'm simply not enthusiastic about giving them hundreds or thousands of more pages to pick through, distort, and lie about."
Romney has already released his 2010 tax returns and an estimate for 2011, with a pledge to release his full returns for last year once they're ready. He filed an extension with the Internal Revenue Service, meaning he may not put out his returns until the October filing deadline.
President Barack Obama's re-election team and top Democrats have been pounding Romney over his tax documents, calling on the presumptive GOP presidential nominee to make public more returns in order to answer questions about offshore accounts and overseas investments.
Defending Romney on a conference call earlier Tuesday, former New Hampshire Gov. John Sununu said each year of Romney's tax returns is about six inches thick. He added if Romney released a dozen years of documents, as some Democrats have would like, then "that'd be about six feet of returns in which they could find whatever...they want to use as a distraction."
Asked why he has not disposed of his offshore accounts, Romney reiterated Tuesday his portfolio is managed in a blind trust that makes it impossible for him to know where his money is invested.
But the former Massachusetts governor did not hesitate to defend offshore investments, specifically naming accounts in the Cayman Islands, one of the countries in which Romney is reported to hold money.
The Republican candidate said the account is established by a U.S. firm to allow "foreign investors to invest in U.S. enterprises and not be subject to taxes outside of their own jurisdiction."
He added: "So in many instances, the investments in something of that nature are brought back into the United States. The world of finance is not as simple as some would have you believe. Sometimes a foreign entity is formed to allow foreign investors to invest in the United States, which may well be the case with the entities that Democrats are describing as foreign accounts."
- CNN's Rachel Streitfeld and Kevin Bohn contributed to this report.