Strong selling in U.S. bank stocks spread to Europe on Friday, where shares of some of the region’s biggest banks suffered their biggest drop in nine months.

The European banking index STOXX fell more than 4% and was on track for its biggest one-day drop since early June, with declines for most major financial institutions, including HSBC, down 4.5%, and Deutsche Bank (ETR:DBKGn), which fell 7.9%.

The shares of the Italian UniCredit (BIT:CRDI) and Intesa Sanpaolo (BIT:ISP) also fell hard.

The global drop in bank stocks was due to Silicon Valley Bank, one of the top banking partners in the U.S. technology sector, being forced to increase its capital after losing $1.800 billion by selling a package of bonds to meet depositors’ cash demands.

Neil Wilson, chief market analyst at Markets.com, said the episode could be “the straw that breaks the camel’s back” for banks, following concerns about rising interest rates and a fragile U.S. economy.

The episode highlighted the vulnerability of banks, many of which were propped up with taxpayer money following the global financial crisis more than a decade ago. That collapse and the economic consequences of the pandemic led central banks and states to inject trillions of dollars to sustain the economy, but now monetary authorities are trying to make amends by withdrawing cash from the market.

Investors in SVB shares had worried about whether the capital increase would be sufficient, given the deteriorating fortunes of many technology companies the bank serves.

SVB CEO Gregory Becker had been calling his customers to assure them their money at the bank was safe, according to two sources familiar with the matter.

But some startups have advised their founders to withdraw their money from SVB as a precaution, the sources added.