FRANKFURT, Germany (AP) -- The European Central Bank says the continent's financial system remains fragile and exposed to risks, including a downturn in markets as well as trouble among banks as they face more bad loans in a weak economy.

The ECB's latest financial stability review said Wednesday that the weakening of the banking sector threatens to cause a flare-up in the 17-country eurozone's 3-and-a-half-year crisis over too much government debt.

The cost of rescuing banks is one of the key sources of the crisis, having overwhelmed the public finances of several European governments.

To ease those concerns, the ECB has pushed for the creation of stronger banking regulation at the EU level that would shield a single government's public finances from the costs of expensive bailouts for banks. Next year, the ECB is expected to take over as centralized banking supervisor.

Because such a system is not yet in place, the ECB emphasized that the current drop in banks' earnings is a key concern. It said the percentage of banks' loans that do not get repaid has risen in several countries, mainly because the economy was weakening.

The ECB said national governments have been too slow in improving growth through reforms that can improve competitiveness.

It also said the financial system could face stress from a sudden reversal of the recent strong gains in markets. Stock and bond markets have rallied globally in recent months as investors cheered the efforts of major central banks to steady the world economy. During such rallies, traders put their money in higher risk investments -- such as stocks -- as they search for higher returns. Interest rates are very low due to benchmark rate reductions by central banks, meaning a savings account would yield very little.

The ECB warned that banks should make sure they have enough financial padding to absorb potential losses in case of a sharp drop in financial markets.

Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.