Republican presidential candidate Mitt Romney has been hesitant to disclose his tax records and personal finances, and now it might be clear why: the former Massachusetts Governor has hidden tens of millions from the U.S. Treasury in secret offshore accounts in the Cayman Islands, according to ABC News.

Offshore accounts used as so-called "tax havens" cost the U.S. over $100 billion a year, and are commonly utilized by the wealthiest citizens and corporations as a means of avoiding U.S. taxes on lucrative profits.

Romney, one of the wealthiest people to ever seek the presidency, said recently he pays about 15 percent of his income in taxes, insisting that he follows all applicable laws. That tax rate is actually much lower than what most Americans pay -- the average U.S. household can expect to pay roughly 19 percent in federal taxes each year, according to the Tax Policy Center, a Washington thinktank.

ABC News noted that Romney has invested over $33 million in more than a dozen funds listed in the Cayman Islands. In addition, their examination of securities records revealed that his former company, Bain Capital, holds 138 accounts in the Cayman Islands.

Romney's campaign told the network that the candidate was simply investing in funds that provided the best opportunity for profits.

"Gov. and Mrs. Romney have money invested in funds that the trustee has determined to be attractive investment opportunities, and those funds are domiciled wherever the fund sponsors happen to organize the funds," a campaign spokesperson told ABC News.

The candidate's tax records have become a subject of recent concern among other Republicans seeking the party's nomination, and Romney was directly challenged by Texas Gov. Rick Perry to release them as soon as possible. Romney said he'd likely do so in April, long after the crucial Republican primary races have ended.