Despite recent improvements in the health of European banks, they remain vulnerable to a daunting array of hazards that are expected to produce another round of sizable write-offs in the next couple of years, the European Central Bank said.

Its report cataloged in detail the problems facing the region’s financial institutions.

The challenges for banks in the 16-nation euro zone include exposure to a weakening commercial real estate market, hundreds of billions of euros in bad debts, economic problems in East European countries, and a potential collision between the banks’ own substantial refinancing needs and government demand for additional loans, the central bank said.

In its twice-yearly review of risks facing the nations that use the euro currency, the central bank expressed particular concern about banks’ need to refinance long-term debt of an estimated 800 billion euros, or $984 billion, by the end of 2012.

European banks will need to set aside an estimated 123 billion euros in 2010 for bad loans, and an additional 105 billion euros in 2011, the report said. That would be in addition to the 238 billion euros they set aside from 2007 to 2009.