PARIS — European banks have to raise about €115 billion ($154 billion) to meet a new standard meant to inoculate the lenders against market turmoil, including bad government debt, a regulator said Thursday.

That's about €8 billion ($10.73 billion) more than what the European Banking Authority previously estimated, and bank stocks around the continent plummeted as rumors of the figure circulated during late trading Thursday.

European banks have billions of euros of risky government bonds on their books, and, as the continent's crisis has deepened, investors have become increasingly concerned the lenders won't be able weather all of the expected losses on those loans. That, in turn, has made banks wary of lending to one another — since they worry that one of their number could go under at any moment. When banks stop lending to one another and businesses, the entire economy seizes up.

In order to restore confidence in the banks and hopefully restart more normal lending, European Union leaders decided in October to force banks to raise more money to reassure markets that they're prepared to weather coming storms.

The EBA said Thursday that the banks need to raise €114.7 billion ($153.8 billion) to meet those requirements. In October, it said it thought banks would need €106.4 billion.

The increase is largely due to a new calculation of the value of the bonds the banks hold: The previous estimate looked at the bonds' June value, while the new one takes into account the prices from the end of September. The value of many of the loans plummeted during the summer.

"These buffers are explicitly not designed to cover losses in sovereigns but to provide a reassurance to markets about the banks' ability to withstand a range of shocks and still maintain adequate capital," the EBA statement said. It said banks should raise the money by first reinvesting profits and reducing bonus payments — cautioning them not to simply sell risky assets, saying that would make markets even more skittish.

Among the hardest hit by the new calculation was Germany, whose banks were asked to raise €13.1 billion — a dramatic increase from the €5.1 billion previously estimated. Now, the EBA says Germany's Commerzbank AG alone will have to raise €5.3 billion in fresh capital. Commerzbank had to be partially nationalized in the wake of the 2008 financial crisis when it failed to raise sufficient capital.

Investors pummeled Germany's hard-hit banks in late Frankfurt trading, with Commerzbank down 9.5 percent, and Deutsche Bank losing 4.3 percent.

But other country's banks need to rustle up even more money, with Greece's in the lead at €30 billion. Next are Spain's, needing €26.2 billion, and Italy's at €15.4 billion. Those figures, however, were largely unchanged from October.

France's banks, by contrast fared better in the latest estimate. They now have to raise €7.3 billion, down from €8.8 billion. Investors still fled their shares, however — a sign that unease in the banking sector still reigns.

Underscoring the pressure on Europe's banks, Standard & Poor's rating agency said Thursday night it is placing long-term credit ratings of 12 Spanish banks under review, saying they could be downgraded.

All but one of those banks and two others will also have their short-term ratings looked at. Two Irish banks were also warned their ratings could be downgraded.

The move comes after the agency put 15 eurozone countries, including Spain and Ireland, on similar notice this week. That has set off a cascade of warnings to banks and other institutions. On Wednesday, France's Societe Generale, Italy's UniCredit SpA and Germany's Deutsche Bank were put on notice.

The money needs to be raised in order for banks to reach a 9 percent core tier 1 capital ratio by the end of June — a measure of how much good capital a bank holds compared with its risky investments. The old requirement was for just 5 percent.

The new rules require banks to fully account for all sovereign debt they hold. Previously, they had been allowed to assume that at least some government debt would be paid in full. That will clearly not be the case: They have already been asked to take substantial losses on Greek bonds, for instance.

Juergen Baetz in Berlin, David McHugh in Frankfurt, Ciaran Giles in Madrid and Frances D'Emilio in Rome contributed to this report.