(Bloomberg News) The U.S. has collected more than $5 billion resulting from taxpayers' disclosures of offshore accounts, the Internal Revenue Service said today.

Taxpayers have made more than 33,000 disclosures, the agency said in a news release.

"People are finding it tougher and tougher to keep their assets hidden in offshore accounts," IRS Commissioner Douglas Shulman said in a statement.

The IRS also announced new procedures to help some U.S. citizens living abroad catch up on their requirements to file U.S. tax returns.

Taxpayers with relatively simple returns who owe $1,500 or less for each of the past few years will be eligible for the program, which starts Sept. 1.

Those taxpayers will be required to file past tax returns and other paperwork showing their account holdings.

The U.S., unlike most other countries, requires its citizens to pay U.S. taxes on the income they earn around the world. They can receive tax credits for payments to other governments.

The IRS news release said some taxpayers have recently become aware of their obligations. That can happen to people who didn't realize that they became U.S. citizens because they were born in the country.

Since 2009, the IRS has run a series of programs encouraging U.S. taxpayers to declare their foreign accounts. Taxpayers must pay penalties for back taxes.

Simultaneously, the IRS and the Justice Department have been pursuing criminal cases against U.S. taxpayers with undeclared assets around the world. Also, in 2010, Congress passed a law requiring non-U.S. financial institutions to provide information to the IRS about their U.S. accountholders.