STORY: Bank stocks around the world plunged on Monday even as President Joe Biden vowed to take whatever action was needed to ensure the safety of the U.S. banking system after the sudden collapse of Silicon Valley Bank and Signature Bank.

Biden's efforts to reassure markets and depositors came after emergency U.S. measures to shore up banks by giving them access to additional funding failed to dispel investor worries about potential contagion to other lenders worldwide.

Until this weekend, the U.S. government had not treated either Silicon Valley Bank or Signature Bank as systemically important.