The head of Credit Suisse Group's largest shareholder, Saudi National Bank (SNB), said on Wednesday it would not buy more shares in the Swiss bank on regulatory grounds. The Saudi bank holds a 9.88% stake in Credit Suisse, according to Refinitiv data. Trading in the Swiss bank's shares was halted late morning as they fell by a fifth to fresh record lows, having been pummelled earlier in the week in market fallout from the collapse of Silicon Valley Bank.