In its ongoing effort to prevent refund fraud, the IRS launched a nationwide crackdown on identity thieves last month.

The "massive national sweep" nabbed 389 identity theft suspects in 32 states, and resulted in 734 enforcement actions -- including 109 arrests and 189 indictments, the IRS announced Thursday.

Check cashers are also being investigated. The IRS said it is visiting 197 of these businesses to ensure they're not helping people get away with identity theft or refund fraud.

Related: Prisoners rake in millions from tax fraud

IRS acting commissioner Steven Miller said he hopes these actions will send a message that the agency is serious about identity theft, which is "one of the biggest challenges facing the IRS today."

"As tax season begins this year, we want to be clear that there is a heavy price to pay for perpetrators of refund fraud and identity theft," said Miller. "This is part of a much wider effort underway for the 2013 tax season to stop fraud."

Related: Victim of identity theft? Expect a long wait for your tax refund

Last year, the IRS stopped $20 billion in fraudulent refunds from being issued -- up from $14 billion in the previous year. The agency also had more than 3,000 employees dedicated to prevent and investigate identity theft-related crimes by late 2012 -- more than double the staffing from 2011.

Meanwhile, 223 identity theft suspects were sentenced to prison in 2012 -- up from 80 in 2011 -- and the average jail time for identity thieves climbed by four months to an average sentence of four years