The problem of too-big-to-fail banks hasn’t gone away, according to the man who ran one of the banks that proved to be too big to fail in 2008.

John Thain, the former CEO of Merrill Lynch, told the Wall Street Journal Friday that “we still have the issue of too big to fail. If anything, the biggest financial institutions are a bigger percentage of the total of the financial industry than they were before.”

“The number of institutions that are really too big to fail is small,” Thain said, “it’s probably less than 10. But we haven’t solved that problem.”

Thain, who resigned from Merrill Lynch shortly after its emergency sale to Bank of America during the height of the financial crisis in the fall of 2008, indicated skepticism that the provisions included in the 2010 Dodd-Frank financial regulation overhaul would be sufficient to prevent big bank failures from threatening the broader system or necessitating bailouts in the future.

“I think that is the key, to have the mechanism to either merge or wind down or break into parts these financial institutions, but in a controlled way, and the mechanism to do that, I think, is not clear yet,” he said.

The administration and financial regulators argue that the Dodd-Frank law provides agencies with the resources necessary to prevent another situation like the crisis of late 2008 and early 2009. Ben Bernanke, the chairman of the independent Federal Reserve charged with implementing many of Dodd-Frank’s rules for limiting banks' risks for the broader economy, acknowledged at a congressional hearing in July that “there is more work to be done before we feel completely comfortable about” big banks. Bernanke claimed that Dodd-Frank provides “a framework for working towards the day, which is not here yet, where we can declare too big to fail as a thing of the past. But we do have some tools now that we didn't have in 2008 and 2009."

Dodd-Frank is still a work in progress. The law firm Davis Polk & Wardwell reported this month that only 40 percent of the law’s required rulemakings have been finalized, and that 60 percent of the 280 past deadlines for regulations have been missed.

According to Dallas Fed president Richard Fisher, fewer than 12 of the largest banks control two-thirds of the assets of the U.S. banking industry, a number that has increased in recent years. The federal safety net for banks’ liabilities has also grown, the Richmond Fed estimated earlier this year. By the end of 2011, almost 60 percent of the banking sector enjoyed a government backstop, two-thirds of it implicit or ambiguously defined.