Italy's government is ready to pump 15 billion euros into Monte dei Paschi di Siena and other ailing banks, sources said, as the country's third-largest lender pushes ahead with a private rescue plan that is widely expected to fail.

The world's oldest bank has until Dec. 31 to raise 5 billion euros ($5.2 billion) in equity or face being wound down by the European Central Bank, potentially triggering a wider banking and political crisis in Italy.

If needed, the government will pump 15 billion euros into the Siena-based lender and several other smaller banks to prevent that, two sources close to the matter said on Thursday.

One source said unlisted regional banks Banca Popolare di Vicenza and Veneto Banca, which were rescued this year by a state-backed fund, would also get support from the state.

The government would make the 15 billion euros available in a decree on Dec. 22, La Repubblica newspaper said on Thursday, adding that Banca Carige could also benefit.

Italy's banking sector is saddled with 356 billion euros of bad loans, around a third of the euro zone's total and a legacy of the 2008-2009 global financial crisis when, unlike Spain or Ireland, Italy did not act to help its banks.

Monte dei Paschi di Siena, advised by investment banks JPMorgan and Mediobanca, plans to raise equity to remove 28 billion euros in bad loans from its books.

Italy's opposition 5-Star Movement has called for JPMorgan's fees to be voided if taxpayers have to come to the rescue.

"We would have never done a deal like that with JPMorgan. In any case we would not pay the commissions (if the bank had to be nationalized," Alessio Villarosa, a 5-Star lawmaker, said.