The two-way battle for control of Bermudan reinsurer PartnerRe has turned hostile, with Italian investment group Exor pressing ahead with its offer despite being rejected.

Exor says its $US6.4 billion ($8.03 billion) cash bid is superior to the share offer from rival Axis Capital and offers a premium on the share price.

PartnerRe and Axis agreed in January to merge. Axis sweetened its offer after Exor, which is controlled by Italy’s Agnelli family, made a counter-bid.

Partner Re and Axis last week reaffirmed their commitment to the merger and announced PartnerRe shareholders will receive a one-off dividend when the deal is completed.

On the same day, Exor said Axis’ revised offer “still undervalues PartnerRe and is clearly not in the best interests of PartnerRe, its shareholders, employees and policyholders”.

Exor says its proposal has no financing conditions, can be completed swiftly and will retain and build upon PartnerRe’s management and employees.