Hedge-fund manager John Paulson has stepped up pressure on Hartford Financial Services Group to split the firm in two in a move that escalates tension between the veteran investor and the 201-year-old insurer.

In a 13D filing Tuesday with the Securities and Exchange Commission, Paulson's Paulson & Co. submitted a letter aimed at rebutting arguments that the company's executives made last week in favour of keeping combined the property-and-casualty insurance business and life-insurance business.