A joint statement from the Swiss National Bank and regulator Finma looked to calm the storm around Credit Suisse, after its share price tumbled by as much as 30%. The slump followed comments from the chair of the Credit Suisse's biggest shareholder, the Saudi National Bank, which ruled out increasing its stake in the Swiss lender.

The two bodies said that they "assert that the problems of certain banks in the USA do not pose a direct risk of contagion for the Swiss financial markets".

"The strict capital and liquidity requirements applicable to Swiss financial institutions ensure their stability. Credit Suisse meets the capital and liquidity requirements imposed on systemically important banks," the statement said.

Ammar Al Khudairy told Bloomberg on 15 March that the bank, which holds a 9.9% stake, would "absolutely not" be investing more money into Credit Suisse, "for many reasons outside the simplest reason, which is regulatory and statutory". He later told Reuters that he supported the bank's turnaround plan.

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Credit Suisse said in a statement: "We welcome the statement of support issued by the Swiss National Bank and the Swiss Financial Market Supervisory Authority Finma."

Credit Suisse had appealed to Swiss financial regulators for a public show of support after its shares hit a new low of CHF1.56, the Financial Times reported, with both the Swiss National Bank and Finma contacted, it said.

The share price slide came in the wake of the collapse of Silicon Valley Bank in the US on 10 March, which has led to fears of contagion across the banking sector after regulators were forced to take control of the lender. Credit Suisse has seen the sharpest fall in share price among its peers but is far from alone in feeling pain from the fallout, with a rout on bank stocks seeing those on the Stoxx 600 lose 16% in the past week.

However, some analysts also suggested that Credit Suisse could need intervention.

"It is looking inevitable that the Swiss National Bank will have to intervene and provide a lifeline," said Octavio Marenzi, an analyst at Opimas. "The SNB and the Swiss government are fully aware that the failure of Credit Suisse or even any losses by deposit holders would destroy Switzerland’s reputation as a financial centre."

At a Morgan Stanley conference on 14 March, Credit Suisse chief executive Ulrich Körner asked for patience on the turnaround and reiterated that the bank's financial position was sound. Chairman Axel Lehmann said at a conference in Saudi Arabia on 15 March that financial assistance from the Swiss government or regulators "isn't a topic" for the lender.

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"We have strong capital ratios, a strong balance sheet,” he said, adding that the bank had "already took the medicine" by unveiling a radical restructuring after years of scandals and underperformance.

"Finma is in very close contact with the bank and has access to all information relevant to supervisory law," the statement from the central banks said. "Against this background, Finma confirms that Credit Suisse meets the higher capital and liquidity requirements applicable to systemically important banks.

"The SNB will provide liquidity to the globally active bank if necessary," it added.

"In a jittery market, following the failure of Silicon Valley Bank in US, Credit Suisse shares have sold off by more than 20% today," Citigroup analysts wrote in a note. "This itself appears insufficient to explain the magnitude of the market move."

Markets have been anxious since the collapse of SVB, but Credit Suisse has struggled against mounting losses and reputational problems over the past two years, including a $5.5bn hit from the collapse of family office, Archegos Capital. It unveiled a second strategy overhaul in the space of two years in October, outlining plans to cut 9,000 jobs and hive off its investment bank into a separate unit called CS First Boston.

In another blow, Credit Suisse cited "material weaknesses" in its financial reporting controls after it was forced to delay the publication of its annual report following a last-minute call from US regulator the Securities and Exchange Commission.

Christian Sewing, chief executive of Deutsche Bank, told the Morgan Stanley conference on 15 March that volatile markets should be "watched closely".

"I think we should also be very clear that there is in my view, no similarity of that, in particular, what we have seen on the West Coast, with that what you see with European banks," he said.

To contact the author of this story with feedback or news, email Paul Clarke