Converium, the struggling Swiss insurer that has launched a deeply discounted Sfr533m (€344m) rights issue, has confirmed that it is being investigated by US regulators.

In a filing with the Securities and Exchange Commission, Converium said that the regulator is investigating possible insider trading ahead of the company's announcement in July of a surprise hole in its reserves. Converium said it has voluntarily responded to the SEC's request and intends to continue to co-operate with the regulator.